[kreig]

Usually there's a 3 day window for the money to settle, if the bank claims that it did not receive the transaction on this time window, they will "deny" the failed transaction and send to the originator a "return"[1] which contains the type and explanation of why did it failed, and the money won't be transferred to the receiver.

If it surpass the 3 day window a "late return" will be sent to notify the origination that the transaction failed, however, the money may already have been transferred to the receiver.

[1]: https://www.moderntreasury.com/learn/ach-return-code-referen...