QuickBooks M-Pesa Workflow Integration

I am looking for an experienced developer to build a middleware integration between QuickBooks Online and M-Pesa for automated supplier payments in Kenya. The system should connect to QuickBooks Online, retrieve approved/unpaid supplier bills and supplier payment details, and allow authorized users to initiate payments directly from the accounting workflow. The middleware should validate the supplier, bill amount, outstanding balance, payment details, and prevent duplicate payments before sending the payment request through the Safaricom M-Pesa B2C API. It should handle the M-Pesa asynchronous callback, capture the final transaction status, M-Pesa transaction ID, conversation ID, result code, and result description, and only mark the supplier bill as paid in QuickBooks after Safaricom confirms a successful transaction. The solution should include secure QuickBooks OAuth authentication, Safaricom Daraja API integration, payment status tracking, transaction logging, error handling, duplicate-payment protection, callback endpoints, and proper reconciliation between the actual M-Pesa payment and the corresponding QuickBooks BillPayment. The middleware should be designed securely and be scalable so that other payment methods such as bank APIs or PayPal can be added in the future.