Integrate MOMO Payment API

I need the MTN MOMO payment API integrated into my custom-built e-commerce website and mobile apps.

Integration is required for:
- Single payments
- Refunds
- Wallet transactions

Apps to be integrated:
1. Vendor App: [6AMMart Store App](https://codecanyon.net/item/6ammart-store-app/36772173)
2. Customer App: [6AMMart Multi-Vendor App](https://codecanyon.net/item/6ammart-multivendor-food-grocery-ecommerce-parcel-pharmacy-delivery-app-with-admin-website/36772112)

Ideal Skills & Experience:
- Proficient in PHP
- Experience with payment API integration
- Familiarity with 6AMMart apps
- Strong problem-solving skills
- Attention to detail