Job Description We are a company developing an online payment application and are looking for an experienced freelancer to integrate our system with digital payment and billing services. The application will support payments for various types of bills, including: Membership fees and recurring dues BPJS and IAR payments Insurance payments Electricity (PLN) PDAM (Water utility) Other utility and service bills The system must be integrated with multiple modern payment methods, such as: Credit & Debit Cards VISA QRIS E-Wallets (OVO, GoPay, and other supported e-wallets) The selected freelancer will be responsible for ensuring that all payment transactions run securely, reliably, and in compliance with digital payment industry standards. Scope of Work Analyze requirements for the online payment system Integrate payment gateway and bill payment APIs Implement transaction flows (inquiry, payment, callback/webhook) Integrate multiple payment methods: Credit/Debit Cards VISA QRIS E-Wallets (OVO, GoPay, etc.) Handle error management, retry mechanisms, and transaction logging Perform testing in sandbox and production environments Provide technical documentation for the integration Required Qualifications Proven experience in payment gateway and online payment system integration Strong understanding of REST APIs, JSON, and HTTP security Experience handling callbacks/webhooks Knowledge of transaction security (API keys, signatures, tokens) Proficiency in at least one backend programming language: Java, PHP, Node.js, or Python Nice to Have Experience integrating QRIS and Indonesian e-wallets Previous work on BPJS, insurance, or utility payment systems Familiarity with payment gateways such as Midtrans, Xendit, DOKU, Tripay, or similar providers Experience with production-scale payment systems Expected Deliverables Fully functional online payment system integration Clean, well-structured, and maintainable source code Technical documentation for transaction flow and APIs Project Duration & Budget Project duration: To be discussed Budget: IDR 10,000,000 – 15,000,000 (Negotiable) If you want, I can also: Tailor this description specifically for a Java-based backend Adjust the scope for larger or smaller budgets Create screening questions to filter qualified freelancers Prepare a milestone-based payment plan Just let me know.