Top payment APIs for UK businesses in 2025: Integration, trends and tips

It’s 2025, and a significant number of shopping carts are still being abandoned due to slow or clunky checkout processes. While this remains a common challenge, it is one that can be addressed through the adoption of advanced payment technologies, particularly payment APIs.

Zooming out, the UK’s digital payments market is projected to reach $447.9 billion by 2025. This represents more than just growth; it's a fundamental transformation, fuelled by a compound annual growth rate exceeding 20%.

In 2023, 48.1 billion payments were processed in the UK alone. Each one represented a moment where a business either delivered a seamless payment experience or risked losing a customer due to friction. With 87% of UK adults now using online banking, 60% engaging with mobile banking, and 40% having fully adopted digital-only bank accounts, expectations around fast, secure, and convenient digital payments are higher than ever.

Payment APIs play a central role in enabling this shift. Acting as a vital link between websites, applications, banks, and processors, they ensure transactions are processed quickly and securely in the background. Whether integrated into a small e-commerce platform or a high-volume enterprise system, the effectiveness of an API implementation can significantly influence customer satisfaction and commercial performance.

What is a payment API and why does it matter?

A payment API (Application Programming Interface) is a structured set of protocols that allows software systems, such as websites, mobile applications, or e-commerce platforms, to communicate securely and efficiently with external payment processing services. In essence, it functions as an intermediary layer, enabling real-time, automated transactions between a business system and financial institutions such as banks, card networks, or digital wallets.

When a transaction is initiated, the payment API manages the entire sequence, from capturing and verifying payment details to authorising and confirming the payment. This process occurs within seconds and typically takes place entirely in the background, allowing the end user to complete the payment without being redirected to a separate interface.

For UK businesses, integrating a payment API provides several operational and strategic benefits:

• Streamlined customer experience through embedded, frictionless checkout flows

• Support for multiple payment options, including debit/credit cards, open banking, digital wallets, and direct debits

• Enhanced compliance and security, supporting standards such as PCI DSS and Strong Customer Authentication (SCA)

• Scalable infrastructure that accommodates growth across digital channels and international markets

In 2025, where transaction speed, user trust, and operational resilience are critical to business success, payment APIs serve as a foundational technology. Rather than being a niche integration, they are now a core enabler of digital commerce, particularly in sectors where high transaction volumes or complex billing models are the norm.

With a clear understanding of what a payment API is, the next step is to explore how payment gateway APIs actually work in practice and why their role is central to building reliable and secure payment flows.

How do payment gateway APIs work?

A payment gateway API securely processes online transactions in real-time by capturing payment details, encrypting sensitive data, verifying funds, and returning an instant approval or decline, all in seconds. This seamless exchange happens between your checkout page, the customer’s bank, and your payment processor.

For UK businesses adopting payment APIs, understanding how this workflow operates behind the scenes is essential. These APIs automate complex steps, including tokenisation, fraud checks, and order fulfilment, reducing manual input while enhancing security and customer experience. Here’s a breakdown of how the process works from click to confirmation:

Step 1: Initiating the API request
Once a customer enters their payment details and confirms the transaction, the payment API captures the relevant information, such as the amount, card details, and billing address, and prepares it for secure transmission.

Step 2: Tokenisation and encryption
To protect sensitive data, the API tokenises the customer’s card details, replacing them with a unique identifier, encrypting the transaction. This means personal and financial data never travels in its raw form, reducing the risk of fraud or interception.

Step 3: Transaction authorisation
The encrypted request is sent to the chosen payment processor (e.g. Stripe, Adyen), which passes it to the customer’s issuing bank. Within seconds, the bank checks the transaction against fraud filters, verifies available funds, and confirms legitimacy before authorising (or rejecting) the payment.

Step 4: Response handling and fulfilment
The payment API receives the authorisation response from the acquiring bank or payment processor and updates all relevant systems in real time. If approved, a confirmation message is displayed to the customer, inventory levels are adjusted, and fulfilment workflows, such as dispatch or digital delivery, can be automatically triggered. This integrated approach supports operational efficiency while ensuring a consistent customer experience.

Key business impacts of payment gateway APIs
Modern payment gateway APIs manage multiple payment methods (cards, digital wallets, bank transfers) within a single integration, reducing manual work and supporting compliance and security at scale. By automating and securing each step, they enable businesses to offer faster, frictionless checkout experiences and keep focused on growth, not payment logistics.

With a clear view of how payment gateway APIs function behind the scenes, it’s useful to explore the different types available. Each approach offers unique benefits depending on the business model, technical infrastructure, and user experience requirements.

Types of payment APIs explained: RESTful, SOAP, and GraphQL

Understanding the core types of payment APIs is essential for organisations aiming to integrate or optimise their business payment systems. RESTful, SOAP, and GraphQL APIs each offer distinct advantages depending on performance requirements, implementation complexity, and data handling preferences.

RESTful APIs

Representational State Transfer (REST) APIs are the most widely adopted, known for their simplicity, scalability, and compatibility with modern web frameworks. They are well-suited to businesses seeking agile integration with minimal overhead, ideal for most e-commerce and SaaS platforms.

SOAP APIs

Simple Object Access Protocol (SOAP) APIs are highly structured and enforce strict messaging standards. They are typically used in enterprise environments where security, reliability, and data integrity are paramount, particularly in financial services and healthcare sectors.

GraphQL APIs

GraphQL allows clients to specify precisely the data they require, which improves efficiency and performance, particularly for mobile platforms. GraphQL provides precise control and flexibility for fintech applications or services that require tailored queries with minimal payloads.

Use cases for payment APIs in the UK

As digital payments become a routine part of how businesses and customers interact, companies in the UK are using payment APIs in increasingly sophisticated ways to drive efficiency, meet compliance standards, and enhance customer experience. From streamlined e-commerce checkouts to personalised financial services and resilient subscription billing, here are practical examples of measurable value across sectors.

E-commerce and embedded checkout

Modern RESTful payment APIs support integrated checkout flows, allowing transactions to be completed without redirection to third-party gateways. This consistency builds trust and reduces friction. UK retailers implementing RESTful APIs have reported conversion rate increases of up to 35%, a significant advantage in competitive online markets.

Open banking and personalised financial services

Open Banking APIs enable authorised fintech providers to securely access users’ financial data (with consent), enabling features such as real-time affordability assessments, automated account verification, and personalised budgeting. SOAP APIs are commonly used in these regulated, high-security contexts due to their structured communication and reliability. Lenders leveraging these APIs have seen application processing times drop by up to 60%, while budgeting apps report improved engagement and retention.

Recurring billing and subscription models

For subscription-based services, ranging from SaaS platforms and gyms to curated product deliveries, Direct Debit APIs offer more stable payment processing than card-based methods. Failure rates are lower, and retry mechanisms can recover up to 70% of declined payments. Some platforms have begun using GraphQL APIs to improve how billing data is queried and displayed, enhancing both performance and user visibility across subscription cycles.

As the demand for instant, always-on digital services grows, another category of payment APIs is becoming increasingly critical: those that support real-time money movement.

What is a real-time payment API?

A real-time payment API enables the instant transfer of funds between bank accounts, 24/7, without relying on card networks, making it ideal for fast, secure, account-to-account payments in the UK. These APIs eliminate settlement delays, aid in automation, and are now more commonly used for payouts, refunds, and B2B transactions where speed is essential.

In the UK, real-time APIs often operate on the Faster Payments Service (FPS), a scheme that has supported near-instant bank transfers since 2008. More recently, Open Banking payment APIs have added a secure and regulated layer, allowing authorised third-party providers to initiate real-time payments directly from a customer’s bank account, with rich data and lower fees.

Adoption is accelerating. In 2024, UK Open Banking payments surpassed 14 million transactions per month, supported by over 100 regulated third-party providers, reflecting a strong demand for fast and transparent alternatives to traditional card-based payments.

How do real-time payment APIs work?

When a real-time payment is initiated through an API, whether via Open Banking or directly through FPS, the process includes validating the transaction, authorising user consent, checking balances, and transferring funds. The result is near-instant confirmation, typically in seconds, with APIs facilitating both the initiation and status tracking of the payment.

Transforming payouts in the gig economy

One of the clearest examples of real-time payment APIs in action can be found in the UK’s gig economy. Consider the experience of a delivery rider or ride-hailing driver finishing a long shift. Traditionally, payouts were processed weekly. With real-time payment APIs, earnings can be transferred directly to the worker’s account within minutes of completing a job.

This isn’t just convenient, it’s materially impactful. For gig workers, immediate access to funds can determine whether essential costs (like fuel or groceries) can be met without delay. In 2023, the UK processed 4.6 billion real-time transactions, a 16% increase from the previous year, underscoring the growing demand for speed and flexibility in digital payments.

Next steps: Turning the payment API strategy into an implementation

As real-time payments become more mainstream, powered by services like FPS and open banking APIs, the question isn’t whether to adopt them, but how to do it effectively. Understanding how payment APIs power real-time, secure, and flexible digital experiences is only half the equation. The next step is to integrate a payment gateway API into an existing business setup, while ensuring security and efficiency.

Here’s what that process looks like for UK-based organisations.

How to integrate a payment gateway API (UK guide)

To integrate a payment gateway API, UK businesses must connect their website or app to a secure payment processor using API credentials, test transactions in a sandbox environment, and configure supported currencies and payment methods. This enables real-time, automated payment flows for e-commerce, SaaS, and subscription models.

While the process may seem technical, most providers offer well-documented SDKs, developer support, and pre-built plugins to simplify integration. This section goes through essential steps, from compliance checks and API key setup to webhook configuration and go-live testing.

Pre-integration checklist: Aligning requirements and readiness

Before starting the integration process, it’s important to clarify the business and technical requirements. Will the system handle one-off payments, subscriptions, or both? Are international transactions involved? What payment methods need to be supported? Cards, bank transfers, digital wallets or more.

It’s also essential to assess your infrastructure. Most modern payment APIs require a secure HTTPS environment, and decisions need to be made about how sensitive payment data will be handled. Fortunately, many providers offer hosted payment pages or tokenisation, offloading the more security-intensive components of the flow.

Authentication and API key management

Before sending live transactions, you’ll need to securely authenticate with your payment provider. Most platforms issue private API keys or OAuth tokens, which your system uses to verify requests. These credentials should be stored in secure server-side environments and never exposed in frontend code. For added security, consider enabling IP whitelisting, setting permission scopes, and implementing key rotation policies to prevent unauthorised access.

Sandbox testing: Safe and simulated transactions

Reputable payment providers offer a sandbox environment, a secure, simulated testing space where developers can build and test payment workflows using mock data.

This allows teams to:

• Validate API integration logic

• Simulate various success/failure scenarios

• Check how payments behave across edge cases (e.g. expired cards, insufficient funds)

This step is essential before going live, ensuring that the payment journey works smoothly and securely under real-world conditions.

Webhook configuration for payment events

To automate workflows like sending confirmation emails or updating order statuses, you’ll need to configure webhook endpoints. These are server URLs that receive real-time event notifications (e.g. payment success, failure, dispute). Leading APIs like Stripe and Adyen provide signature verification for webhook calls, helping you confirm authenticity and protect against spoofing. Set up retry logic to handle temporary outages and log events for auditing.

Post-integration monitoring and reporting

Once your integration is live, ongoing monitoring is critical. Use your provider’s dashboard or internal observability tools to track key metrics: transaction success rates, declined payments, API response times, and error codes. Many platforms also support automated alerts for anomalies or fraud attempts. Monitoring allows you to respond quickly to issues and continually optimise the checkout experience.

PCI DSS responsibilities

Even when using tokenisation or hosted payment pages, UK businesses must comply with Payment Card Industry Data Security Standards (PCI DSS). Choose a provider that helps reduce your compliance burden (e.g. via SAQ A scope), but still ensure internal policies align, including how you store logs, handle access controls, and manage third-party tools.

Once integration is in motion, the focus naturally shifts to another critical area: security and compliance. In a regulatory environment as rigorous as the UK’s, it’s not just about making payment APIs work; it’s about ensuring they function safely, securely, and in line with all legal obligations. Let’s take a closer look at how modern APIs handle these challenges.

International payments and currency management

Despite changes post-Brexit, international payments remain a key priority for UK businesses. Payment APIs now offer built-in support for multi-currency transactions, enabling merchants to accept payments in local currencies while receiving settlements in GBP.

Leading platforms such as Adyen and Wise offer APIs that support features like:

• Real-time foreign exchange (FX) rates

• Local payment method compatibility (e.g. iDEAL in the Netherlands, SEPA in the EU, Konbini in Japan)

• Transparent fee structures

• Compliance with cross-border regulatory requirements

For UK-based e-commerce platforms and service providers, this capability reduces complexity and expands market reach without the overhead of manually managing multiple financial integrations.

Payment API security and compliance for UK businesses

Security remains one of the most pressing concerns for businesses adopting digital payment infrastructure. While integration may seem like the most complex part, ensuring compliance with UK and international security standards is equally important. Fortunately, modern payment APIs are designed with security at their core, not as an afterthought, but as a fundamental requirement.

PCI-DSS: The industry gold standard

The Payment Card Industry Data Security Standard (PCI-DSS) outlines strict requirements for handling cardholder data. Any business processing card payments must comply, but the good news is that reputable payment API providers typically handle most of the heavy lifting. Hosted payment pages, tokenisation, and secure data transmission protocols are all designed to minimise exposure and ease the compliance burden.

Strong Customer Authentication (SCA): Reducing fraud risk

Strong Customer Authentication, mandated under the UK’s implementation of PSD2, introduces an extra layer of protection for electronic payments. It typically involves two-factor authentication, such as entering a one-time code sent via SMS. While SCA can sound complex, most APIs now include SCA-compliant flows by default, reducing the development effort and enhancing trust at checkout.

GDPR: Protecting personal data

With the General Data Protection Regulation (GDPR) firmly in place, businesses are responsible for how they collect, process, and store customer data. Leading payment APIs incorporate GDPR principles into their architecture, including data minimisation, access controls, and clear consent mechanisms.

Tokenisation is also key here. As mentioned earlier, it replaces sensitive card data with unique, encrypted tokens. Even in the unlikely event of a breach, attackers would only find meaningless placeholders instead of real card numbers — a critical safeguard in the UK’s tightly regulated data landscape.

With the technical, regulatory, and security fundamentals in place, the next step is choosing the right payment API solution. Not all providers are created equal, and selecting one that aligns with the business's size, needs, and future plans can make a significant difference to both user experience and operational efficiency.

How to choose the right payment API for your UK business

The best payment API for your UK business is one that aligns with your growth goals, supports real-time transactions, and integrates seamlessly with your tech stack. Look for providers that offer developer-friendly documentation, strong support, and scalability as demand grows. The right payment API should support your business model, help you stay compliant, and adapt to customer needs as your business grows.

Scalability: Planning for growth

It's essential to assess not only how the API performs today but how well it can support long-term growth. Some providers are well-suited for early-stage businesses but may struggle under enterprise-scale transaction volumes. Others are designed for high throughput from the outset but may have minimum usage thresholds or pricing tiers that don’t suit smaller operations. Consider future expansion plans when evaluating scalability.

Developer experience and support

Developer documentation, SDKs, and onboarding tools play a crucial role in successful implementation. While some providers offer robust technical documentation, hands-on support can vary. Access to technical support, SLAs, and even dedicated account managers should be factored in, especially when timely troubleshooting is critical to business continuity.

Real-time capabilities

In 2025, real-time features, such as instant transaction confirmation, real-time balance updates, and fast settlement, are becoming standard expectations. APIs that support these functions can significantly enhance customer experience and internal cash flow visibility.

Ecosystem compatibility

A payment API must integrate smoothly with the rest of the business’s ecosystem, from accounting platforms like Xero or QuickBooks to CRMs, ERP systems, and inventory tools. API flexibility and available integrations can reduce operational overhead and streamline reconciliation and reporting.

Choosing the right payment API is about more than just cost or convenience; it's about selecting a long-term partner that can evolve with the business. Evaluating these factors carefully will ensure a resilient and future-ready payment setup.

Top 5 payment APIs for UK businesses in 2025

With a growing number of providers offering advanced payment functionality, selecting the right API can feel overwhelming. The key is to match your business needs, whether that’s subscriptions, high-volume transactions, or Open Banking innovation, with the provider’s strengths. Below are five standout payment APIs that are shaping the UK market in 2025.

Stripe: A developer-focused powerhouse

Stripe remains a top choice for businesses prioritising flexibility, speed, and developer experience. Its API is highly customisable and well-documented, supporting everything from simple payments to complex, multi-party marketplaces.

• Ideal for: Startups, SaaS platforms, marketplaces
• Key features: Advanced API tooling, broad global support, built-in fraud protection
• UK pricing: 1.5% + 20p for UK cards; 2.5% + 20p for international cards

Adyen: Built for enterprise-scale operations

Adyen offers an end-to-end payment platform with full control over the payment flow, from acquiring to fraud detection. It’s particularly well-suited to larger businesses that want to optimise costs through the Interchange++ pricing model.

• Ideal for: Large enterprises and international retailers
• Key features: Global reach, unified commerce (online and in-store), in-house risk tools
• UK pricing: Interchange++ (typically 11p + 0.60% plus scheme fees)

GoCardless: Subscription billing made simple

GoCardless focuses on recurring payments, making it a go-to for subscription-based businesses. Its direct debit-first approach ensures lower fees and higher success rates for regular billing. More recently, it has added support for instant bank payments via Open Banking.

• Ideal for: SaaS, memberships, service-based businesses
• Key features: Optimised for UK Direct Debit, Open Banking integration, retry mechanisms
• UK pricing: 1% + 20p per transaction, capped at £4

Worldpay: A trusted industry veteran

Worldpay offers robust support for omnichannel payments, backed by decades of experience. Its APIs enable seamless transactions across online, mobile, and in-person channels. With support for multiple acquirers, it offers businesses more flexibility in managing merchant relationships.

• Ideal for: Retailers with both physical and digital presence
• Key features: Omnichannel support, trusted brand, strong UK presence
• UK pricing: Varies by package and volume; typically available on request

Wonderful: Instant payments with purpose

Wonderful stands out by combining modern payment tech with a strong social impact ethos. They provide Open banking-powered payments through QR codes and payment links, enabling instant bank-to-bank transfers, bypassing card networks entirely.

• Ideal for: SMEs, ethical brands, charities, and purpose-driven enterprises
• Key features: Instant payments and settlement, no integration fees, built-in fraud protection
• UK pricing: From £19.99/month for up to 2,000 transactions (+VAT); no card processing fees
• Unique value: Profits help fund free fundraising tools for UK charities

The future of payment APIs: Trends shaping 2025 and beyond

As we look ahead, payment APIs are moving well beyond simple transaction handling. The next phase is more integrated, more intelligent, and far more exciting. Here are the trends defining their future:

Open Finance: Beyond the bank account

Open Banking was just the beginning. Now we’re entering the era of Open Finance, where APIs connect not just bank accounts but also pensions, mortgages, insurance, and investment platforms. Imagine applying for a mortgage and allowing your lender instant access to your financial picture, from spending patterns to savings, across all providers. It's faster, safer, and radically more transparent.

Smarter payments with AI

Artificial intelligence is no longer limited to fraud prevention. In 2025 and beyond, AI will help predict and optimise payment behaviour. Think automated retries for subscription payments timed to when customers are most likely to have funds, or personalised checkout flows that suggest the best payment method based on historical usage.

Everything happens in real-time

Real-time payment is becoming the norm, not the exception. By 2028, the UK is projected to see over 6.3 billion real-time transactions, driven by evolving customer expectations and better infrastructure. Instant payouts, real-time refunds, and on-the-spot reconciliation will define the next generation of payment APIs.

The rise of embedded finance

Payment APIs will become invisible. Embedded finance is enabling payments to happen within context, in the background of everyday activities. From ordering coffee within your banking app, to paying for fuel via your car’s dashboard, or splitting a bill by simply scanning a QR code at your table, payments will feel seamless and intuitive.

Power your business with smarter payment API integration

We’ve covered a lot of ground, from understanding how payment APIs work, to choosing the right provider and peering into the future of digital payments.

To recap:

• Focus on user experience and payment flexibility

• Prioritise security and compliance (PCI-DSS, SCA, GDPR)

• Look for scalability and integration with your tech stack

• Align with providers whose values match your business goals

Whether you’re a fast-moving startup, a growing SME, or an enterprise streamlining global operations, payment APIs are no longer just a backend tool, they’re a strategic business driver. The question isn’t whether payment transformation is happening. It’s whether your business is ready to lead it.

FAQ

Which is the best payment API for UK small businesses?

Wonderful is a great choice for small UK businesses, low fees, no hidden costs, and easy setup. Stripe and GoCardless are also strong options, depending on your use case.

What are the main benefits of using a payment API for my business?

Payment APIs enable faster transactions, better user experience, automated reconciliation, and support for multiple payment methods, all while reducing manual errors.

How can UK businesses integrate a payment API with QuickBooks or Xero?

Many APIs, including Wonderful, offer built-in or third-party integrations with QuickBooks and Xero, enabling real-time syncing of transactions and simplified accounting.

Can I use a payment API for international transactions from the UK?

Yes. Payment APIs like Stripe and Adyen support international payments, currency conversion, and local payment methods, ideal for UK businesses going global.

Do I need a developer to set up a payment API in the UK?

Not always. Some APIs, like Wonderful, offer low-code or no-code options with simple onboarding. However, more complex custom integrations may require developer support.

Are payment APIs secure and compliant with UK regulations?

Reputable APIs follow PCI-DSS, GDPR, and Strong Customer Authentication (SCA) standards. Wonderful, for example, uses open banking for secure, compliant payments.

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