8 Best Credit Card Processing APIs for Your Business in 2025

The great thing about e-commerce payment technology is that it’s relatively easy to customize. All you need is some experience using Application Programming Interfaces (APIs) – or a willingness to learn – and a credit card processor that offers this helpful development toolkit.

With that being said, not every payment processor offers an API. Those that do rarely provide adequate documentation to properly implement their API, or their API only supports a few coding languages. Even if a merchant services provider offers great value in other areas, not having the tools you need to build custom e-commerce integrations and applications can be hugely limiting.

After researching dozens of credit card processing services, I’ve put together a list of those that offer a great range of APIs to help you get the most out of their respective software suites.

Overall, I found that Leaders Merchant Services (LMS) offers the best APIs of all the payment processors on this list. In addition to offering multiple developer toolkits, including a free one, it provides all the necessary documentation and a sandbox testing environment. LMS’s API library also contains plenty of built-in security features.

What We Look For in the Best Credit Card Processing APIs

Not every developer kit and API library is built equal. That’s why I made sure every payment API on my list offers these features.

• Comprehensive documentation. Having well-written and detailed documentation means you don’t have to spend hours trying to decipher API code, error responses, and access tokens.
• Wide range of supported languages. A well-built API should support multiple programming languages, regardless of the software that will connect to the API. The more languages that a payment processor’s developer kit supports, the better.
• Sandbox. A sandbox lets you test your API in a sandbox environment so you can make sure it works before you deploy it to your working environment. This means you’re not risking harming your customers’ e-commerce experience by testing your API on your live website.
• Security. Because the API will be handling sensitive financial data, the payment processor needs to ensure it is built with a security-first approach. This includes enforcing the use of hashing, SSL certificates, and developer authentication via API access tokens.
• PCI compliance support. Every API offered by a payment processor needs to be PCI-compliant. However, if you’re using the API to build checkouts that are hosted on your website, you’ll have to fill out a different questionnaire to ensure that you’ve met testing and security requirements. Your payment processor should offer support with this.

1. Leaders Merchant Services: Low Rates With Multiple API Options

While many payment processors choose to utilize just one API solution, Leaders Merchant Services (LMS) offers multiple developer toolkits. You can pay for the popular Authorize.net payment gateway’s developer kit or get Google Pay’s API for free. With Google Pay being one of the most trusted names in modern payment technology, this can help you reassure those customers who don’t always trust third-party payment gateways.

LMS’s rates are some of the lowest in the industry, starting at only $9.00/month. Being able to use the Google Pay API for free makes this payment processor a great budget-friendly solution. It’s not as comprehensive or detailed as Authorize.net’s API, but it still has all the features you’ll need to build custom payment solutions.

Google Pay’s API has a decent amount of documentation for web or Android applications. There’s a tutorial to show you how to download and deploy the Google Pay API and a checklist to help you test an application before deployment. However, Google Pay’s API doesn’t support development on iOS.

Features and Benefits

• Recurring billing. With Authorize.net’s API, you can easily create, update, and cancel subscriptions. You can also create subscriptions directly from existing customer profiles to save time and speed up service. The API allows you to access a list of up to 1,000 subscriptions in a single request, with filters for customized search results. This simplifies subscription management, especially for larger businesses.
• Transaction reporting. Transaction reporting through the Authorize.net API keeps you informed about your sales. The API offers comprehensive access to transaction history, enabling batch settlement, batch statistics access, and retrieval of transaction lists, among other operations.
• Pre-built Google Pay buttons. Though you’ll have to adhere to Google Pay’s branding standards to use its API, you can customize the Google Pay button that appears on your site. You can change text, language, color, and sizing before copying and pasting the code directly into your website.
• Payment card recognition. Google Pay’s API allows customers to use their device’s camera to capture their card details. This makes paying for your products or services quick and convenient and can lead to fewer abandoned carts, particularly because customers don’t need to have the Google Pay digital wallet for this to work.

Read our in-depth Leaders Merchant Services review for more details.

2. Paysafe: Robust API & International Support

Paysafe stands out with its robust proprietary API that covers payments, wallets, value-added services, reporting, and more features to enhance and customize your payment processing experience. You can integrate multiple of the 250+ payment methods that Paysafe offers through a single endpoint.

Paysafe is excellent for software platforms because it enables you to create a white-labeled merchant onboarding experience using a single REST-based API call. The processor handles the infrastructure and account approval processes and provides a payment experience that aligns with your branding. This feature is critical for businesses looking to offer seamless payment solutions to their customers without managing complex regulatory requirements.

Paysafe is also ideal for businesses selling high-value items at low volumes, such as art, luxury goods, cars, and furniture. This is because Paysafe offers lower-than-usual interchange rates starting at 0.50% + $0.10 per transaction and provides robust international support across 120 markets. Its APIs for local payment methods and multiple currencies make it easy to expand globally.

Features and Benefits

• Embeddable PCI-compliant payment form. You can use the Paysafe JS API to create a custom payment form that integrates smoothly with your site. It ensures data security and PCI compliance, letting you focus on designing the user experience that matches your site’s aesthetics.
• Split payouts. This Paysafe API is crucial for businesses that must distribute payments across multiple accounts. If you manage different departments with separate ledgers, this API simplifies payment distribution, refunds/credits, and fund retrieval between accounts.
• Balance transfers between linked accounts. This API facilitates the seamless transfer of funds between linked merchant accounts. It’s particularly useful for businesses that need to issue credits to merchants, such as for promotional activities.
• Clover API. If you purchase Clover equipment through Paysafe, you’ll get access to the robust Clover API to customize your POS system with features for managing employees, inventory, payments, and more. Clover’s API also lets you create subscriptions and plans and offers e-commerce support.

Check out our detailed Paysafe review for more information.

3. Stax: Secure, Well-Documented API for High-Volume Businesses

Stax’s documentation library is among the most comprehensive I’ve seen from a payment processor. It covers everything from setting up a sandbox environment to using its JavaScript library (Stax.js). You can also use Stax’s PCI-compliant framework as a base to add custom-built features like multi-currency transactions – something that Stax doesn’t normally offer.

Stax’s API is Level 1 PCI-compliant and has a variety of built-in security features like rate limiting, tokenization, and address verification (AVS). The Stax.js library also contains multiple validation events that can protect your databases from injection attacks by ensuring that only data that meets the expected input is pushed to your database.

On top of that, you don’t need to pay any extra fees to use Stax’s modern software or developer kit thanks to its simple subscription-style pricing starting at $99.00/month. Compared to other payment processors, Stax’s low per-transaction fees of 8¢ + interchange (in-person) could result in savings of up to 40%. However, its pricing model only works for US-based merchants processing at least $8,000 monthly transactions.

Features and Benefits

• Embeddable payment forms. Some customers will abandon their cart if they’re redirected to the webpage of a third-party gateway when it’s time to pay. Stax.js allows you to embed a payment form into your website to reduce cart abandonment and improve trust with your customers.
• Language agnostic. Stax’s API is designed to work with any language that can interact with REST API, enabling you to use this API with a wide variety of software suites.
• Custom integrations. You can create webhooks to send data from the Stax API (and vice versa) to third-party business tools like QuickBooks Online, MailChimp, and Zapier, among others.
• PCI compliance support. Merchants using self-hosted payment APIs usually have to undergo a lengthy assessment. With Stax, you’ll get access to a third-party PCI compliance dashboard that will alert you when your security assessment is due and guide you through the questionnaire.

Read our expert Stax review to discover more great payment features.

4. Chase Payment Solutions: A Variety of APIs for SaaS Companies & SMBs

Chase Payment Solutions offers a variety of proprietary and third-party APIs that cater to Software as a Service (SaaS) companies and small and medium-sized businesses (SMBs). SaaS companies can use WePay’s developer kits to custom-brand Chase’s payment solutions. WePay’s comprehensive developer tools and documentation allow you to create and integrate customized payment solutions with no overhead and minimal development effort.

For SMBs, Chase offers APIs for the Orbital gateway and virtual terminal, digital wallets, and other e-commerce solutions. With the Orbital gateway and virtual terminal, you can integrate payment processing in various card-not-present environments, including websites, mobile, call centers, and mail-order departments. You can also automate recurring payments. This versatility enables you to provide a seamless payment experience across all channels.

Chase Payment Solutions doesn’t work with high-risk merchants. However, low to mid-risk businesses can benefit from its competitive pricing model, which includes no monthly fees and transaction fees starting at 2.6% + 10¢. You can enjoy same-day payouts with a Chase business checking account at no additional cost and next-day payouts as standard, even without a Chase bank account.

Features and Benefits

• Loyalty programs. For SMBs aiming to enhance customer loyalty, Chase’s Pay with Chase Points loyalty program has a wide appeal due to its large consumer base. You can enroll Chase cardholders into rewards programs through the Pay with Points APIs, let them see their points balances, and redeem their points to complete purchases.
• OptBlue. This program allows businesses to accept American Express transactions, which are typically more expensive, at competitive rates.
• Secure account data sharing. The Account Data Sharing APIs offer a secure method to connect your customers’ Chase accounts to your proprietary applications. This feature enables customers to quickly consent to sharing their account data, which is then protected through tokenization, ensuring data security while providing a custom-branded payment experience.
• Reliable screening. SaaS companies can benefit from Chase’s MATCH screening and receive a list of positive hits to offboard. MATCH screening helps in evaluating merchant risk by screening merchants against a comprehensive database of businesses with prior account terminations, providing the reasons for the terminations and offering an additional layer of security in making onboarding decisions.

Check out our Chase Payment Solutions review to find out more.

5. ProMerchant: Integrations With Trusted APIs for All Kinds of Transactions

ProMerchant integrates with Authorize.net, which offers a comprehensive API full of helpful developer tools. You can build digital wallets and use SDKs to integrate payment forms into your sales channels or use its pre-built, mobile-friendly payment forms. Authorize.net also offers a virtual terminal to key in payments via phone, email, mail, or text.

Alternatively, you can process mail order/telephone order (MOTO) payments using the free Payments Hub virtual terminal. You can get a free Payanywhere card reader, which gives you access to additional APIs and SDKs for e-commerce and mobile apps. With ProMerchant’s free Ingenico hardware, you can access even more developer-friendly APIs.

ProMerchant is ideal for businesses that sell both in-person and online. Its interchange-plus plans start at $7.95 and are some of the industry’s lowest. However, its transaction fees of 3% + 10¢ (credit) are slightly higher than LMS’s fees. If you run a restaurant or retail business, you can opt for its zero-cost processing program.

Features and Benefits

• Customize your terminal. Opting for the free Ingenico Desk 3500 gives you access to Ingenico’s cloud and on-terminal APIs, enabling you to build a feature-rich POS suited to your business’s needs. Standout on-terminal APIs include surcharging, asset tracking, and customer surveys.
• Free (custom-branded) mPOS. Payanywhere’s SDKs allow developers to integrate mPOS features into any iOS or Android device at no extra cost. You can also use Payanywhere’s APIs to embed payment processing features into your proprietary apps. This means you can offer secure payment processing under your branding without revealing that you’re using a third-party processor.
• Customer profiles. With Authorize.net’s API, you can store customer billing, payment, and shipping details. For about 25¢ per update, you can refresh credit card data, reducing payment interruptions.
• Simple checkout. With Authorize.net’s API, you can add a “Buy Now” button to your website for a frictionless payment experience.

To see more benefits, take a look at our full ProMerchant review.

6. Flagship Merchant Services: Cheap API and High-Risk Merchant Accounts

Flagship Merchant Services offers the popular Authorize.net payment gateway and API for significantly less than some competitors. It only charges $7.95/month to use Authorize.net, which is almost 70% cheaper than its regular price. But you’d have to pay extra for full access to Authorize.net’s software and Flagship’s in-house support. If you opt for the free Clover Mini POS or buy Cover devices through Flagship, you’ll also get the robust Clover API.

Starting at $7.95/month, Flagship’s plans include the essentials. This approach means you’ll never pay for features you don’t need. However, it can prove costly if you do need a range of features. Flagship’s per-transaction interchange rate of 3.58% + 0.19¢ (in-person) is fairly high compared to other processors, but you can negotiate your fees for a better rate. If it can’t at least match your current rate, you’ll receive a $200 AMEX gift card under its Meet-or-Beat guarantee.

Flagship boasts a 98% approval rate. This means it will likely accept your application even if you’re a new business with no credit history, have a low credit score, or operate in a high-risk sector like cannabis, multi-level marketing (MLM), and travel and hospitality.

Features and Benefits

• Easy invoicing. Authorize.net allows you to send email invoices using a “click to pay” link, along with reminders for unpaid invoices.
• Automatic recurring billing. Using Authorize.net’s API, you can set up monthly or custom automatic billing monthly. This removes the need to re-enter customer information and ensures you always get paid on time, boosting your cash flow.
• Manage customers, employees, and inventory. Efficiently create, update, and manage customer profiles with Clover’s API. You can also create employee profiles and assign them shifts and orders. For inventory management, Clover’s APIs enable you to add inventory items, create item groups, and assign tags and modifiers, among other capabilities.
• Accept gift cards. Clover’s API makes it easy to process both physical and virtual gift cards, reload them, and view balances.

See our comprehensive Flagship Merchant Services review for a full fee breakdown.

Other Notable Credit Card Processing APIs

7. Payment Depot

Payment Depot offers third-party APIs such as the Authorize.net payment gateway and virtual terminal, as well as popular shopping carts and e-commerce platforms. Its API toolkit allows you to efficiently manage payments on your website, through mobile devices, or at physical locations, ensuring a smooth customer experience and streamlined operations​​.

It’s important to note that Payment Depot works only with high-volume small businesses processing at least $8,000 in card sales per month. If your business processes a high volume of transactions, you could see significant savings with its flat monthly subscription starting at $0. But it might prove expensive for small, low-volume businesses. Additionally, the processor doesn’t work with high-risk merchants.

8. Square

You can use Square’s proprietary APIs to build versatile credit card processing solutions, including online, mobile, and in-person commerce. You can leverage Square’s extensive developer toolkit to meet unique business needs with white-label payment solutions. Whether customizing Square for your use, publishing in the Square App Marketplace, or collaborating with Square sellers, its comprehensive platform supports many functionalities.

However, Square’s lack of a thorough vetting process may result in sudden account terminations, particularly for high-risk merchants. Additionally, you may encounter challenges reaching customer support after account deactivation and experience funds being held for months, posing operational and cash flow risks.

Which Is the Best Credit Card Processing API?

If you want to build custom e-commerce features, you’re going to need a well-documented and comprehensive credit card processing API that you can easily integrate with your current e-commerce solutions.

Leaders Merchant Services (LMS) is the best choice for most small businesses, including those processing a lower volume of card sales. It offers some of the industry’s lowest interchange-plus pricing, and you can negotiate your rates and tailor your plan. While LMS charges a fee for using Authorize.net’s API, you can use Google Pay’s API for free, which is a great way to keep your costs down.

If your business is growing and you’re expanding into international markets, I recommend Paysafe. This processor makes it easy to accept multiple currencies and payment methods. You can integrate many of its 250+ supported payment methods through a single endpoint. Software companies aiming to create white-labeled payment solutions and small businesses selling high-value items seeking secure and sophisticated payment experiences can benefit from Paysafe’s robust proprietary APIs.

ProMerchant is a great option for businesses that operate both in-person and online. It offers integration with the trusted Authorize.net API, which provides access to additional security features. It also provides a virtual terminal through Authorize.net and Payments Hub at no extra cost. Additionally, you’ll receive free POS hardware to support your in-person operations. The hardware brands that ProMerchant works with, like Ingenico and Payanywhere, offer additional APIs to customize your POS system.

FAQ

What is a payment gateway API?

A payment gateway API is a relatively short section of code that allows your payment gateway or payment processor to integrate with another software. These APIs allow merchants to build custom payment forms and shopping carts. Some processors like Stax develop their own APIs and include them for free – this ensures that the API works seamlessly with their software while also saving you money.

Which credit card processing API is best?

It depends on your needs. Leaders Merchant Services (LMS) offers a few developer toolkits, such as the comprehensive Authorize.net API and the free Google Pay API. Authorize.net’s API is fully documented, includes some advanced security features, and allows you to build custom payment solutions. LMS’s custom pricing model means you only pay for Authorize.net when necessary, saving money if the free Google Pay API meets your requirements.

What’s the difference between a payment gateway and a payment processor?

A payment gateway captures and transmits payment information between your point of sale (whether that’s in-person or online) and the payment processor. The processor then relays this information from the customer’s bank to the merchant’s bank. Some payment processors develop their own payment gateways, while others like ProMerchant offer merchants a third-party gateway that connects to their processing service.

Which payment gateway is most popular?

PayPal and Stripe are two of the best-known payment gateways, but they’re not always the best choice for your business. They typically charge higher-than-average fees and they don’t come with additional processing features you might need, like card terminals and third-party POS integrations. Many of our top 10 credit card processors in 2025 have their own payment gateways or use industry-leading third-party solutions, despite being considerably cheaper.