Senior Fintech Architect and Developer for Phased Checkout, Collections and Digital Wallet Platform

Project Overview We are looking for an experienced fintech full-stack developer or small development team to build a phased financial technology platform. The project will be delivered in two separately priced and independently deployable phases: Phase 1: Checkout & Collections A cardless merchant payment and collections platform. Phase 2: Digital Wallet A customer and merchant wallet built on the same secure core platform. Phase 1 must be capable of going live without waiting for Phase 2. Applicants must therefore design the architecture so that the wallet can be added later without rebuilding the checkout and collections platform. Phase 1 — Checkout & Collections The first phase should include: merchant registration and onboarding; KYC/KYB document upload and review; merchant dashboard; admin portal; static and dynamic QR payment requests; payment links; payment references; invoice-style collection requests; partial and full payment tracking; USSD integration; Newland N950 smart-terminal support; customer payment pages; receipts and notifications; settlements and reconciliation; refunds and reversals; merchant staff roles and permissions; transaction and audit logs; reports and exports; merchant and customer aliases linked to verified backend identities; English and Setswana; accessibility features, including read-out support, simple instructions, icons and large-button mode; AI-generated expense and collection summaries and cost-saving suggestions. The platform must support low-connectivity and low-literacy users and must not require customers to open a wallet before paying a merchant. Phase 2 — Digital Wallet The second phase should include: customer wallets; merchant wallets; wallet registration and verification; available, pending, held and reserved balances; wallet funding; wallet withdrawals; wallet-to-wallet transfers; wallet-to-merchant payments; QR and USSD wallet access; beneficiary management; transaction PIN and OTP confirmation; transaction history and statements; transaction fees and limits; reversals and refunds; wallet reconciliation; wallet administration and monitoring; future agent and interoperability readiness. The wallet must use a proper controlled financial ledger. Wallet balances must not be stored only as editable balance fields. Applicants should have experience with double-entry ledger or equivalent immutable financial-ledger architecture. Technical Requirements The solution should include: secure backend APIs; web-based merchant and admin portals; mobile-responsive customer interfaces; Android smart-POS integration; multi-tenant architecture; role-based access control; MFA for privileged users; encrypted data in transit and at rest; secure API-key and secret management; signed webhooks; idempotent transaction processing; duplicate-payment protection; complete audit trails; transaction-state management; secure QR and payment-link generation; separate development, staging and production environments; automated testing and deployment; backup and recovery; monitoring and alerting; full technical and user documentation. The platform must be designed for future PCI DSS and PCI Secure Software Standard/PCI S3 readiness. Phase 1 will not store raw card numbers, CVV, PIN blocks or other card-authentication data. Architecture Deliverables Before full development begins, the selected applicant must provide: proposed technology stack; system architecture; database design; transaction-flow diagrams; wallet-ledger design; API structure; user and role matrix; security architecture; USSD integration design; N950 integration approach; deployment architecture; phased milestone plan. Deliverables The contractor must provide: complete source code; frontend and backend applications; database schema; APIs and webhooks; merchant portal; admin portal; customer interfaces; N950 application or integration; USSD integration; automated tests; deployment scripts; technical documentation; API documentation; administrator and merchant guides; production deployment; post-launch bug-fix support. All source code must be committed from the beginning to a repository controlled by the client. All custom code, database designs and paid project deliverables will belong to the client. Applicant Requirements Applicants should have proven experience in several of the following: fintech platforms; payment processing; digital wallets; double-entry ledgers; transaction-state machines; settlement and reconciliation; QR payments; USSD integrations; Android smart-POS terminals such as Newland, PAX or Sunmi; secure APIs and webhooks; KYC/KYB workflows; multi-tenant SaaS; audit logging; financial-system security. Please do not apply based only on general website or mobile-app development experience.