Money sent to you by mistake isn’t a gift. It’s a test with a notification.

A wrong transfer arrives looking like luck and is really somebody else’s money sitting in your account. The temptation is strong because nobody has asked for it yet and you did nothing to cause the error, which makes keeping it feel passive rather than chosen. Spending it is the decision, even though it never feels like one.

Say something the same day, to the person or to the app, before the number starts feeling normal. Move it out of your spending account while you sort it out. Keeping somebody’s mistake costs more than the amount, and usually later.