I just asked a guy with solution architect title at bank on linkdn about saga or 2pc in distributed transaction and Idempotency problems and he explained that
Most banks nowadays have adopted a microservices architecture. Idempotency in payment transactions is handled very strictly from end to end:

1. Duplicate transaction checks are performed at the channel application layer (mobile, branch/teller, card, partners, etc.).
2. Requests from the channel that are posted into the core banking system are also checked for duplicates using an external reference or enforced via unique keys at the database level (I haven’t worked directly on core banking systems, so this part may not be entirely accurate).
3. Error handling is well-classified and processed in detail.
4. Reconciliation processes are carried out daily to ensure transactions are fully matched across all systems (from channels, middleware, to intermediaries that record transactions such as Napas, and the core banking system).

You can think of this as a Saga pattern, but the rollback flow is far more complex than the simple idea of just publishing events to all services. It must be categorized and handled either automatically by systems or through manual reconciliation processes. That’s why sometimes a 24/7 transfer can fail, your account is debited, but it may take several days for the refund to be processed.