Experienced Payment Integration Specialist — Global Payments, Crypto, Regional Wallets

Project type: Fixed-price, milestone-based Experience level: Expert Budget: May exceed CHF 2'000 in total, with CHF 100–300 per payment integration. Project Overview: We are looking for an experienced payment systems developer to build a standalone international payment platform that can be connected to different shopping websites or applications. Our goal is to accept the widest practically available range of online payment methods worldwide, including credit/debit cards, PayPal, cryptocurrencies, and popular regional or national payment systems. We are NOT looking for someone whose experience is limited to integrating Stripe, PayPal, or standard e-commerce plugins. We need a specialist with proven experience integrating different payment providers, regional payment networks, digital wallets, and cryptocurrency payment solutions. We prefer using existing, reliable APIs, SDKs, and open-source solutions rather than developing standard functionality from scratch. 1. Payment Platform, Database and API The developer will build an independent payment platform, including: • A standalone, customer-facing payment checkout page. • Support for multiple payment methods, currencies, and providers. • A secure database recording orders, transactions, payment statuses, currencies, and provider references. • Automatic payment detection, verification, and confirmation. • API endpoints and webhooks for communication with external websites and applications. • A basic administration interface for managing payment methods, providers, routing rules, and transactions. • Modular architecture allowing additional payment methods to be integrated easily. The platform must accept payment requests from external applications, process payments, store transaction information, and securely return payment results. The shopping website itself and its integration with this payment platform are outside the scope of this project. These will be handled separately. However, the developer must provide clear API documentation and a working test example demonstrating how an external application can create a payment request and retrieve its status. 2. Payment Methods A. International Credit/Debit Cards and PayPal Support major international card networks, including Visa, Mastercard, American Express, and other relevant networks where available. PayPal must also be supported. We consider the possibility of using several payment processors for the same payment method, such as: • Stripe • Worldline / SIX-related acquiring solutions • Direct bank acquiring, where available • Other suitable payment processors The platform must support configurable routing between providers. For example, 30% of eligible card transactions could be processed through Stripe and 70% through another provider. This distribution must be configurable without modifying the application code. B. Direct Cryptocurrency Payments We want to accept major cryptocurrencies directly into wallets under our control, without mandatory intermediary cryptocurrency payment processors or unnecessary processing fees. We prefer existing, proven, open-source solutions rather than custom development of standard blockchain payment functionality. Examples worth evaluating include BTCPay Server, PayRam, and other suitable self-hosted projects. Required functionality: • BTC, ETH, USDT, USDC, and other widely used cryptocurrencies on relevant networks. • Automatic transaction detection and blockchain confirmation. • Payment identification and matching to the correct order. • Wallet addresses, payment amounts, and QR codes. • Automatic recording of payments in the database. • API/webhook communication with external applications. • Support for adding further currencies and blockchain networks. We do not require cryptocurrency exchange, trading, fiat conversion, or custodial services. C. Regional and National Payment Systems A major objective is to support payment methods that are particularly popular in specific countries and regions. Below are the examples. Europe: TWINT (Switzerland), Swish (Sweden), Vipps/MobilePay (Nordic countries), BLIK (Poland), iDEAL/Wero (Netherlands and other European markets), Bancontact (Belgium), Bizum (Spain), MB WAY (Portugal), Satispay (Italy), and others. Russia: MIR cards, SBP, and SberPay. Asia: Alipay, WeChat Pay, UnionPay (China), UPI and RuPay (India), PayPay (Japan), Kakao Pay and Naver Pay (South Korea), GCash, Maya, PromptPay, GrabPay, QRIS, DuitNow, and other regional systems. Americas: Pix and Elo (Brazil), Mercado Pago (Latin America), Interac (Canada), and other relevant local payment methods. Other regions: M-Pesa and other African mobile payment systems, mada and other Middle Eastern payment networks, and additional regional methods recommended by the developer. This list is not exhaustive. The developer is expected to identify important regional payment methods and recommend the most efficient ways to integrate them. 3. Administrative Guidance and Provider Onboarding This is an essential part of the assignment. The developer must have practical knowledge of the requirements for activating different payment methods. For each proposed integration, we expect guidance on: • Which payment provider, bank, or organization must be contacted. • Whether a separate merchant account or agreement is required. • Necessary documentation and approval procedures. • Availability for international merchants. • Supported countries and currencies. • Setup costs, subscription fees, and transaction fees. • Technical and commercial limitations. We will handle merchant registrations, contracts, and banking arrangements ourselves. The developer should identify any merchant eligibility or onboarding requirements before starting the corresponding integration. 4. Database, Security and Documentation The system must correctly store: • Payment request and order identifiers. • Payment method and processing provider. • Amount, currency, and payment status. • Provider transaction references. • Blockchain transaction references where applicable. • Payment confirmation timestamps. • Refunds, adjustments, and relevant processing fees. • Information necessary for reconciliation and auditing. It must handle duplicate notifications, delayed confirmations, failed transactions, and other common payment scenarios. Sensitive card data must not be stored on our servers. The developer must provide complete source code, database documentation, API documentation, and deployment instructions. The platform and its infrastructure must remain under our control. 5. Project Milestones and Payment We prefer fixed-price milestones. Phase 1 — Core Payment Platform Development of the standalone checkout, database, administration interface, APIs, and modular payment architecture, including fully functional integrations of the most widely used international payment methods: • Credit and debit cards (Visa, Mastercard, American Express, etc.) • PayPal • Cryptocurrencies (BTC, ETH, USDT, USDC, etc.), preferably using existing open-source solutions for direct wallet payments without intermediaries. Fixed budget: CHF 1200 for the complete Phase 1 scope. Payment will be released upon successful implementation, testing, and delivery of all Phase 1 functionalities, including working payment integrations, accurate transaction recording in the database, and complete technical documentation. Phase 2 — Individual Payment Integrations Each payment method or provider integration will be treated as a separate milestone. Our budget is CHF 100–300 per integration, depending on its complexity. We strongly prefer leveraging existing APIs, SDKs, open-source software, or already integrated payment providers to minimize unnecessary development costs. We are interested in efficient integration of existing solutions, not unnecessary development from scratch. Milestones will be paid after the agreed functionality is implemented, successfully tested, and documented. 6. Required Experience Applicants must have demonstrated experience with: • Multiple international payment gateways and acquiring APIs. • Regional and national payment methods. • Digital wallets and mobile payment systems. • Direct cryptocurrency payments and self-hosted solutions. • Multi-provider routing and payment orchestration. • Payment APIs, webhooks, transaction databases, and reconciliation. • Merchant onboarding and payment provider requirements. • Secure production payment infrastructure. Experience limited to installing Stripe Checkout or standard payment plugins is insufficient. 7. Questions for Applicants Please answer the following: 1. Which international and regional payment methods have you personally integrated into production systems? 2. Have you implemented multiple payment providers for the same payment method, including configurable traffic distribution? 3. Which existing open-source solutions would you recommend for direct cryptocurrency payments? 4. Which regional payment methods have you integrated, particularly TWINT, Alipay, WeChat Pay, Pix, UPI, BLIK, or Swish? 5. How would you design a standalone payment platform that can be connected to different websites through an API? 6. Can you guide us through merchant account activation and provider onboarding? Please provide specific examples of previous projects. We are looking for a long-term technical partner who understands international payment processing, can recommend practical solutions, and can progressively expand the platform with additional payment methods.