Flow Diagram: High Fault-Tolerance Strategy

The diagram shows the three main mechanisms for determining the final payment status and how they work together to ensure fault tolerance:

1. Payment Initiated (Start Point)
   This is when the customer starts a payment process.
2. Three Parallel Status Sources
   1. Frontend Redirect Status (B):
      After payment, the user is redirected to the merchant’s page with status info.
      → Requires parameter validation to prevent tampering.
   2. Backend Notification (C):
      Fiuu sends a server-to-server callback to the merchant backend.
      → Must validate source IP or signature.
   3. Status Inquiry API (D):
      Merchant actively calls Fiuu’s API to check status if delays occur.
3. Validation Steps
   1. Frontend → Validate parameters.
   2. Backend → Validate source authenticity.
   3. Inquiry → Re-query until status is confirmed.
4. Match Results (H)
   Combine results from these sources.
   Rule: If at least two out of three match, confirm the transaction.
5. Final Confirmation (I)
   Merchant updates internal system and informs the customer.

Why This Matters?

• If one method fails (e.g., backend callback delayed), the other two can still confirm the payment.
• This reduces risk during partial outages or network issue.