The system can’t do that. As a matter of fact I know someone who works for a French bank, and they fucked up and created a bunch of money. They had to work overnight with a bunch of accountants going through the books to make sure they reverted everything.

EDIT: apparently they use some old XML protocol, where twice a day a correspondant bank send them a list of accounts to debit or credit. They didn’t send something once, so my friend’s bank just replayed the previous settlement list.