How do you handle a scenario when an external bank is unavailable?

When an external bank is unavailable, it is important to ensure the stability and correctness of the system. Main approaches:

• Retry implementation with exponential backoff to avoid overloading the service and allow time for recovery.
• Timeouts to prevent long process blocking.
• Error handling and user notification about temporary service unavailability.
• Fallback logic, such as using cached data or alternative channels.
• Asynchronous request processing with subsequent notification of the result.

Example: when paying through an external bank, if the service is unavailable, you can put the transaction in a queue and retry later, notifying the user about the delay.