With 52 of Europe’s 121 fintech unicorns based in the UK, B2B payment APIs are essential for businesses looking to increase efficiency, reduce expenses, and streamline payments. The UK B2B payments market is expected to double in size by 2033, from its 2024 valuation of $110.91 billion. However, 51% of business-to-business invoices are still past due, underscoring the pressing need for sophisticated payment methods. For marketplaces, SaaS providers, and companies handling supplier payouts, the correct payment API can revolutionise processes and improve cash flow visibility.

The top 5 UK-focused B2B payment APIs for 2025 are highlighted in this guide, which was chosen based on the APIs’ developer-friendly design, scalability, regulatory compliance, and market reputation. Let’s examine their attributes, costs, and what makes each a top option.

Why Your Business Needs a Modern B2B Payment API

Finance teams are burdened by traditional payment methods, which slow growth due to their high fees, three-day delays, and manual procedures. Modernising your business requires sophisticated B2B payment APIs. They allow you to:

• Automate Payments & Reconciliation: Your finance team can concentrate on more strategic tasks by doing away with manual data entry and errors.

• Get Paid Faster: To achieve near-instant settlements and significantly improve cash flow, use UK-centric rails like Open Banking and Faster Payments.

• Simplify International Trade: Avoid the bad exchange rates and unstated costs of traditional banks by handling multi-currency payments with ease.

• Ensure Effortless Compliance: Assign the workload associated with intricate regulations such as the FCA and PSD2, guaranteeing that every transaction is safe and in compliance.
• Own Your User Experience: To boost conversion rates and foster trust, integrate slick, branded payment flows straight into your platform.

The right API choice accelerates cash flow, enhances user experience, and reduces operational costs.

Top 5 B2B Payment APIs for UK Businesses in 2025

Provider	Best for	UK bank coverage	Developer experience	Pricing structure
Finexer	UK SaaS, marketplaces embedding Pay by Bank	99% of UK banks via Open Banking	Fast onboarding, branded flows	Usage-based, no setup fees
Stripe	Tech startups, SaaS, and marketplaces	Supports payments via FPS, Bacs, and Open Banking; UK card payments accepted	Extensive SDKs, robust docs	1.4% + £0.20 per UK card txn
Adyen	Large enterprises, global retailers	Local acquiring in 30+ countries, including the full UK coverage	API-first and customisable	Custom pricing, scalable
Airwallex	UK businesses scaling globally, fintechs	Local settlement in 14+ currencies, 160+ local payment methods in 180+ countries	RESTful APIs, SDKs, sandbox access	Competitive fees starting at 1.3% + £0.20 for UK cards; no hidden FX conversion fees when using Airwallex Wallet
Checkout.com	High-volume merchants, fintech platforms	Multi-currency support with global acquiring, including UK coverage	Modern APIs, fraud prevention	Tiered usage pricing

Finexer

Finexer is an FCA-authorised payment API with a focus on the UK that specialises in Pay by Bank solutions through Open Banking. It offers a fully white-label platform perfect for SaaS, marketplaces, and fintech apps that integrate UK bank payments, as well as instant settlement through Faster Payments.

Implementation: With thorough RESTful APIs and a testing sandbox, integration is rapid. Webhook notifications, batch payment support, and branded payment flows are all offered by Finexer. Onboarding usually takes days rather than months, and its documentation is developer-friendly.

Pros:

• 99% of UK banks are covered by Open Banking.
• Usage-based pricing that doesn’t charge for setup or cancellation
• Real-time payment status updates and instant settlement
• Completely white-label processes for smooth branding.
• High compliance with FCA and PSD2

Cons:

• Newer in the market but growing fast in the UK.

Why should you choose Finexer?

Businesses can easily accept direct bank payments from 99% of UK banks with Finexer. Our Open Banking platform is built for speed, security, and scalability, which will help you save money while providing your clients with a flawless payment experience.

What’s so special about Finexer?

• Pay-by-bank transfers to 99% of UK banks are covered.
• Cost-effectiveness: Clear, usage-based pricing; No Setup Fees, only pay for what you use.
• Instant Settlement: Real-time transfers allow you to receive your money more quickly.
• Compliance: For total peace of mind, it was constructed with full FCA and PSD2 compliance.
• Onboarding: Exceptionally fast setup with committed assistance.

Reasons why:

• Speed: Near-real-time confirmation and instant settlement.
• Trust: PSD2-compliant and FCA-regulated for assured security.
• Flexibility: Pricing based on usage that grows with your company.
• Control: To preserve your identity, use white-labelled, branded flows.
• Coverage: One of the market’s widest reaches, with access to 99% of UK banks.

Stripe

Stripe is a well-known international payments platform with strong UK-specific features like Open Banking add-ons, Bacs, and Faster Payments. It provides a wide range of payment methods and currency support for SaaS companies, startups, and marketplaces.

Implementation: Stripe provides open APIs with copious documentation and comprehensive SDKs. Rapid development is made possible by its well-supported sandbox environment. Custom checkout processes, subscriptions, and financial links are supported by integration for instantaneous account verification.

Pros:

• supports a wide range of payment methods and more than 135 currencies.
• Top-notch development tools and libraries
• robust compliance and fraud protection (PCI DSS, SCA)
• scalable from small businesses to major corporations

Cons:

• With extra conversion fees, pricing can be complicated.
• Technical resources are needed for complete customisation.

Adyen

Adyen is a payment processor with an enterprise focus that provides multi-currency settlements, unified commerce with local acquiring, and effective risk management. It is well-liked by major UK and foreign retailers.

Implementation: With customised onboarding and comprehensive documentation, Adyen offers a versatile API-first platform. It integrates with intricate enterprise architectures and facilitates the acceptance of payments via multiple channels. Although implementation times vary, professional assistance is beneficial.

Pros:

• Global presence combined with strong local acquisition
• scalable to extremely high volumes
• All-inclusive risk and fraud instruments
• Extremely adaptable API

Cons:

• More expensive, usually for larger businesses
• More intricate integration and onboarding procedures

Airwallex

A robust payment API is provided by the international fintech platform Airwallex, which aims to streamline both domestic and international business-to-business transactions. It is perfect for UK businesses expanding internationally because it supports local currency settlements and multi-currency wallets and integrates with well-known e-commerce platforms.

Implementation: RESTful APIs, hosted payment pages, mobile SDKs, and no-code eCommerce plugins are just a few of the integration options that Airwallex offers. Fast onboarding and flexible control over payment experiences are made possible by the platform’s sandbox environments and thorough developer documentation.

Pros:

• offers competitive FX rates and supports payments in more than 20 currencies.
• In large markets, local settlement lowers conversion costs.
• Adaptable integration: hosted page, SDK, API, and plugins
• PCI DSS compliance and robust fraud detection
• A multi-currency wallet that allows you to store and pay in different currencies

Cons:

• An authorised EMI rather than a bank specifically subject to FCA regulation
• Integration of advanced features may necessitate technical resources.
• Fees in some corridors are marginally higher than those of strictly local providers.

Checkout.com

Checkout.com offers real-time analytics, sophisticated fraud prevention, and API-first payment processing. It is designed for fintechs and high-volume retailers in the UK and accepts a variety of currencies and payment methods.

Implementation: Checkout.com facilitates modular payment flows with comprehensive API documentation and developer tools, making it simple for companies to set up fraud policies and international payments. Sandbox environments make testing easier.

Pros:

• Robust fraud detection driven by AI
• accepts international payment methods and multiple currencies.
• scalable for high volumes of transactions
• Clear and open fee schedule

Cons:

• Smaller businesses may possess less access to pricing.
• For full feature utilisation, technical sophistication is required.

How to Choose the Right Payment API for B2B

The effectiveness of your payment processing, compliance, and general customer experience can all be greatly impacted by your choice of the best B2B payment API for your UK company. When assessing payment processors and APIs, keep the following points in mind:

Integration Speed: Seek out payment APIs that provide thorough, thoroughly documented RESTful APIs with sandbox settings. This configuration speeds up your go-to-market strategy and cuts down on developer onboarding time. Rapid integration capabilities guarantee that your teams can swiftly automate B2B payment processing and settlement workflows while reducing project risk.

Pricing Transparency: Select suppliers who offer usage-based, transparent pricing structures free of hidden costs. Adopting embedded payments in your platform is made easier with transparent pricing, which includes startup discounts and no setup or cancellation fees. Keep a close eye on foreign exchange rates, transaction fees, and any monthly minimums related to payment gateway APIs.

Regulatory Compliance: For reliable payment processor APIs operating in the UK market, regulatory supervision by the FCA, compliance with PSD2, and Strong Customer Authentication (SCA) are non-negotiable. To prevent fraud, foster trust with partners, and process Open Banking payments smoothly while adhering to legal frameworks, make sure the API you have selected satisfies all of these requirements.

Customisation & Branding: To preserve your brand identity during the payment process, search for white-label payment APIs for embedded B2B payments. The user journey is improved, payment drop-off rates are decreased, and conversion rates are raised with customisable payment flows and branded checkout experiences. Delivering consistent experiences across web and mobile platforms is another benefit of using APIs that facilitate multi-channel integration.

Support for Multiple Currencies and Automation: Choose platforms that offer features like automated invoice reconciliation and batch payments, as well as support for multi-currency payment APIs. This facilitates seamless cross-border transactions and lessens manual labour, which is particularly crucial for UK companies with global operations.

Support & Experience for Developers:

Your integration will function seamlessly and grow with you if you have a strong developer ecosystem, which includes sandbox environments, SDKs, clear documentation, and quick technical support. The adoption of sophisticated features like subscriptions, recurring billing, and real-time transaction reporting is accelerated, and downtime is decreased by seamless API integration.

Conclusion

The key to increasing growth and enhancing cash flow in the UK market is selecting the appropriate B2B payment API. A brief synopsis of the top providers discussed is as follows:

• Finxer: 99% UK bank coverage, instant Pay by Bank payments, best for UK SaaS and marketplaces.

• Stripe: Perfect for new businesses and tech firms, offering worldwide support for FPS, Bacs, and Open Banking.

• Adyen: Enterprise-grade, scalable, and available in more than 30 countries for local acquisition.

• Airwallex: With more than 160 payment options and multi-currency support, Airwallex is ideal for UK companies expanding internationally.

• Checkout.com: Developed for large retailers, this platform provides multi-currency international purchasing and sophisticated fraud protection.

Selecting any of these modern, compliant, and developer-friendly APIs will streamline payment workflows, reduce costs, and enhance user experience.