Finality does not exist in payments

From the article:

What does a transaction being “final” mean? In the layman’s use of the term, it means that the transaction cannot be reversed.

As a payments professional, finality can be thought of more as a probability distribution given the technical/organizational infrastructure which was used to make a payment (the “rails”), the facts of the underlying transaction, the relationship of the parties, and the governing law(s) and regulatory regimes. We can confidently say things like “wire transfers are more final than credit card payments” but we generally don’t say “wire transfers are final.” If they were really final, the world would break.

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A “hold harmless” is a very, very brief conversation between two peers at different institutions which is then memorialized on paper. The peers are generally operations professionals, one at the receiving institution and one at the sending financial institution (and sometimes even at its customer, since many serious users of financial infrastructure have operations teams to interact with their providers). The conversation is often shockingly informal, on the level of “Yeah we goofed and sent you $1.2 billion to the wrong account. Mondays, am I right?”, and the operations professionals make a verbal agreement about disposition of the transaction in minutes (or less).