What if you don’t notice either? Is an accidental mistake in a transaction a crime for the beneficiary even if they have no idea it happened? That seems ridiculous to assert so, to me.
From a moral standpoint, I agree that if you know you’re being given something you don’t deserve, the moral thing (in my own morality, which I would not impose on others without their agreement) would be to speak up and correct the mistake.
However from a legal standpoint, I think that you cannot criminalize someone for a mistake made by someone else, and you often cannot prove that they know about the mistake, so making a law based on what someone knows seems like a bad idea that would be unenforceable in many cases and cause social distress in others (imagine being forced to testify that a friend confided in you that they didn’t speak up when someone overpaid them), so I would hope that the law would clearly acknowledge that there can be innocent mistakes and people are not to be criminalized for not speaking up when benefiting from someone else’s mistake.
At least on a personal level. On a corporate level, I think there should be a correction against the likes of credit card companies, utilities, banks and insurance companies whom individuals depend on to be very upstanding, yet who can and do make a lot of profit by sloppy bookkeeping, difficult billing practices, obscure complicated bills, avoiding paying money due with complex processes and rules, excessive fees and fines, etc.