Banking Transaction Processing Issue – Incorrect Balance & Duplicate Transactions

[Hamzayy01]

🐞 Issue Summary

There is a problem with the banking transaction processing system where user balances are updated incorrectly, and in some cases, duplicate transactions are recorded.

📌 Expected Behavior

• Each transaction should be processed exactly once.
• User balance should be updated accurately after each successful transaction.
• Failed transactions should not affect the balance.

❌ Actual Behavior

• Some transactions are processed multiple times (duplicate entries).
• User balance becomes inconsistent after retries or network failures.
• In certain cases, failed transactions still modify the balance.

🔁 Steps to Reproduce

1. Log in as a user
2. Initiate a payment/transfer
3. Simulate a network failure or retry the request
4. Check transaction history and balance

💥 Impact

• Users may lose trust due to incorrect balances
• Financial inconsistencies in the system
• Potential risk for real-world financial errors

🛠 Possible Causes

• Missing idempotency checks for transactions
• Backend does not properly handle retries
• Lack of transaction locking or atomic operations

✅ Suggested Fixes

• Implement idempotency keys for all payment requests
• Ensure database transactions are atomic
• Add validation to prevent duplicate processing
• Improve error handling and rollback mechanisms

🧪 Environment

• Backend: (e.g., Node.js / Django / etc.)
• Database: (e.g., MongoDB / PostgreSQL)
• Browser: (if applicable)

📎 Additional Notes

• Logs show repeated API calls for the same transaction ID
• Issue appears more frequently under slow network conditions