Do you know about idempotency of payments and how you solved the double payment problem?

Idempotency of payments means that a repeated request for payment with the same parameters will not lead to a double charge.

The problem of double payment arises due to repeated requests (for example, due to network failures or repeated button presses).

Solutions:

• Using a unique transaction identifier (idempotency key), which the client generates and sends with the request.
• The server stores the transaction status by this key: if a request with such a key has already been processed, the reprocessing does not occur, and the result of the first operation is returned.
• Transactions are recorded in the database with this key, preventing duplication.

Example:

1. The client sends a payment with idempotency_key = "abc123".
2. The server checks if there is a record with "abc123".
3. If not — it processes the payment and saves the result.
4. If yes — it returns the saved result without re-deducting.

This ensures safety against double payments.