Integrate PayPal Gateway to Web/Mobile App

PayPal Payment Gateway Integration

I am looking for an experienced developer to integrate PayPal payment gateway into my existing web/mobile application.

Requirements

- Integrate PayPal Checkout into the existing application.
- Implement secure payment initiation and processing.
- Support PayPal account payments and available card payment options.
- Create and manage PayPal orders through the backend.
- Implement payment approval and capture flow.
- Handle successful, failed, cancelled, and pending payments.
- Verify payment status securely through PayPal APIs.
- Implement PayPal webhooks for reliable transaction status updates.
- Store transaction ID, order ID, payment amount, currency, and payment status in the database.
- Automatically update the related order/subscription after successful payment.
- Handle duplicate payments and interrupted transactions properly.
- Implement refund functionality if required.
- Configure PayPal Sandbox for testing and then assist with production setup.
- Keep PayPal Client ID, Secret, and other credentials secure on the backend.

Technical Requirements

- PayPal REST APIs/SDK.
- Backend integration and payment verification.
- Webhook implementation.
- Secure API credential management.
- Proper error handling and transaction logging.
- Integration with the existing web/mobile application without affecting current functionality.

Deliverables

1. Complete PayPal integration.
2. Backend payment APIs.
3. PayPal webhook implementation.
4. Success, failure, cancellation, and pending payment handling.
5. Sandbox testing.
6. Production configuration.
7. Updated source code and basic integration documentation.

The developer should have previous experience with PayPal payment integration and be comfortable working with an existing application and backend.