Payment Gateway

Custom Payment Gateway Integration

We design and implement secure, scalable payment flows tailored to your business. From one-time charges to recurring subscriptions, with multi-currency support, fraud prevention, and PCI DSS compliance.

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The challenge

Accepting payments online seems simple until you need to do it right

Integrating a payment gateway goes far beyond adding a "Pay" button. It means designing a payment flow that maximizes conversion, complies with PCI DSS regulations, handles refunds and disputes automatically, supports multiple currencies and local taxes, prevents fraud with 3D Secure and machine learning, and scales without manual intervention. The decisions you make in your payment architecture determine your conversion rate, fraud exposure, and ability to expand into new markets.

Every market has its own particularities. In Spain, Redsys is the dominant gateway processed by most banks, and Bizum has become an essential payment method for local commerce. Internationally, Stripe offers the best developer experience and widest coverage of global payment methods. Adyen is the choice for enterprise companies needing a single integration point for all markets. PayPal remains relevant for consumer trust and buyer protection programs.

Payment flow design has a direct impact on conversion. An optimized checkout reduces cart abandonment, a smart retry system recovers failed payments, and card tokenization enables frictionless recurring charges. Refund and chargeback management needs automation to avoid becoming an operational burden that scales linearly with transaction volume.

At Soamee we have integrated payment gateways across very different projects: from ElDomi, a delivery platform with Stripe Connect for split payments between restaurants and riders, to GolfyApp, an app with in-app purchases and recurring subscriptions, to Cawa, a marketplace with payments between buyers, sellers, and the platform. Each project requires a different payment architecture, tailored to the business model.

PCI

PCI DSS Compliance

135+

Currencies supported

Auto

Automated refunds

3DS2

3D Secure 2.0

Architecture

Payment flow design

Every stage of the payment flow optimized to maximize conversion and minimize fraud.

Optimized checkout

Payment form design that minimizes friction: card auto-detection, real-time type recognition, inline validation, and support for local payment methods. Embedded checkout on your site or redirect to provider payment page depending on the case. Continuous optimization with A/B testing to improve conversion rate. Apple Pay, Google Pay, and one-click methods to reduce steps.

PCI DSS compliance

Implementation that complies with PCI DSS standards without your server touching card data. Client-side tokenization (Stripe Elements, Redsys iFrame, Adyen Drop-in) ensures sensitive data never passes through your infrastructure. This allows you to operate at SAQ-A compliance level, the simplest, avoiding costly audits. End-to-end encryption on all communications.

Multi-currency & taxes

Support for charges in multiple currencies with automatic conversion or local pricing. Dynamic calculation of VAT, sales tax, and other taxes based on buyer location. Integration with tax compliance services like TaxJar or Stripe Tax to automate fiscal compliance in the EU (OSS), US, and other markets. Electronic invoicing in local formats as required by regulation.

Refunds & disputes

Automated full or partial refund flows directly from your admin panel. Chargeback management with automatic response that includes order evidence (tracking, delivery confirmation, communications). Early dispute alerts via Stripe Radar or your acquiring bank alert system. Configurable refund policies by product, category, or period. Refund and dispute ratio reporting.

Fraud prevention

Machine learning from Stripe Radar, Adyen Risk Engine, or Redsys anti-fraud module to detect suspicious transactions in real time. Custom rules based on your business behavior: geolocation, purchase velocity, device fingerprint, browser fingerprinting. Adaptive 3D Secure 2.0 that only requests additional authentication when risk justifies it, minimizing friction for legitimate transactions.

Recurring billing

Payment method tokenization for recurring charges without users re-entering their data. Smart retry management for failed payments (dunning): different schedules, alternative methods, and user notifications before suspending service. Automatic prorations for mid-cycle plan changes. Integration with billing systems like Stripe Billing or custom invoicing to generate receipts and invoices automatically.

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Providers

Payment gateways we integrate

We work with the leading payment gateways. We help you choose the right combination for your business.

Stripe

The most complete gateway for digital businesses. Industry-reference API, Stripe Elements for embedded checkout, Stripe Connect for marketplaces with split payments, Stripe Billing for subscriptions, Stripe Radar for ML-powered fraud prevention, and Stripe Tax for automatic tax compliance. Support for 135+ currencies and 50+ payment methods. Our first recommendation for most projects.

Redsys

The dominant payment gateway in Spain, processed by most Spanish banks (CaixaBank, BBVA, Santander, Sabadell). Essential if your main audience is Spanish and you want the best commission rates with your bank. REST API integration with tokenization for recurring charges, 3D Secure 2.0, and virtual POS. Bizum support as a payment method within the Redsys flow.

Adyen

Unified enterprise payment platform. A single contract and API to accept payments worldwide with local methods (iDEAL, Bancontact, Boleto, WeChat Pay). Advanced risk engine with machine learning. Ideal for companies operating in multiple countries needing consolidated reporting, treasury management, and payment routing optimization to maximize acceptance rates.

PayPal

The most recognized online payment method globally. Buyer protection that builds trust. PayPal Checkout for quick payments without entering card details. Venmo for the US market. PayPal Braintree as a full gateway with card, PayPal, and local method support. Ideal as a complementary payment method alongside Stripe or Redsys.

Bizum

The most popular mobile payment method in Spain with over 25 million users. Direct integration for e-commerce through Redsys or as an independent method. Instant payment from the bank app without entering card details. Conversion rates above 90% with Spanish audiences. Essential for any business targeting Spanish consumers.

Hybrid solution

In many projects, the best option is combining multiple gateways. Stripe as the main gateway for international cards and subscriptions, Redsys to optimize commissions with Spanish banks, Bizum for the local market, and PayPal as a trust option. We design the architecture so switching between gateways is transparent, with intelligent routing that selects the optimal provider.

Success stories

Projects with payment integration

Payment solutions in production with real transaction volume.

ElDomi

Delivery platform with Stripe Connect for managing split payments between restaurants, riders, and the platform. Real-time payments, automatic commissions, and scheduled payouts to each marketplace party.

Stripe Connect split payments

GolfyApp

Golf app with in-app purchase system and recurring subscriptions. Apple Pay and Google Pay integration for one-tap payments. Trial management, upgrades, and cancellations with RevenueCat and Stripe.

In-app purchases + subscriptions

Cawa

Carbon credits platform with marketplace payment system. Transaction management between buyers, sellers, and the platform with escrow, conditional fund release, and real-time financial reporting.

Marketplace payments + escrow

Technologies

Payment tech stack

Tools and technologies we use to build robust and secure payment infrastructure.

Stripe API Stripe Elements Stripe Connect Redsys REST Adyen Drop-in PayPal SDK Node.js TypeScript Python PostgreSQL Redis Webhooks React Next.js Docker AWS Terraform RevenueCat

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FAQ

Frequently asked questions about payment integration

Which payment gateway should I choose for my business?

It depends on your target market and business model. If you primarily operate in Spain and want the best commission rates with your bank, Redsys is the natural choice. If you sell internationally or need advanced features like subscriptions, marketplace payments, or ML-powered fraud prevention, Stripe is the best option. For enterprise companies with multi-country operations, Adyen offers a unified platform. In many cases, the best strategy is combining multiple gateways: Stripe as primary and Redsys/Bizum to optimize the Spanish market.

Do I need to comply with PCI DSS to accept card payments?

Yes, but the compliance level depends on how you integrate payments. If you use client-side tokenization (Stripe Elements, Redsys iFrame, Adyen Drop-in), card data never touches your server and you only need SAQ-A compliance, which is a simple self-assessment questionnaire. If you process card data on your server, you need SAQ-D certification, which is much more demanding and costly. We always implement the integration so that your server never touches sensitive payment data.

How does 3D Secure 2.0 work and does it affect conversion?

3D Secure 2.0 (3DS2) is the authentication protocol that verifies the cardholder's identity. Unlike the previous version, 3DS2 allows "frictionless" authentication where the bank approves the transaction without user intervention based on risk data. Only higher-risk transactions require active authentication (SMS code, fingerprint). We implement 3DS2 adaptively: mandatory when risk requires it, frictionless when the transaction profile is low risk. This minimizes conversion impact while complying with PSD2/SCA regulation.

How much does it cost to integrate a payment gateway?

A basic Stripe or Redsys integration with checkout, webhooks, and order management can be implemented in 2-4 weeks (5,000-15,000 euros). An advanced integration with multi-gateway, subscriptions, marketplace split payments, multi-currency, custom fraud prevention, and financial reporting can require 6-12 weeks (20,000-50,000 euros). Cost also depends on your business model complexity: a simple e-commerce is different from a multi-vendor marketplace or a SaaS platform with usage-based billing.

How are refunds and chargebacks managed?

We implement automated refund flows from your admin panel, supporting both full and partial refunds. For chargebacks, we configure automatic responses that collect and send order evidence to the bank (delivery confirmation, customer communications, tracking). We also implement early alerts through Stripe's dispute system or pre-chargeback alerts to resolve claims before they become formal disputes. A good prevention system reduces chargebacks to a minimum.

Let's start

Let's integrate payments into your platform

We help you choose the right gateway, design the payment flow, and build a secure, scalable payment integration.

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