The former is a gift, while the latter is a fee.
exactly this
a zap implies a different sort of relationship vs a tip. thanking someone for something with something of value vs a monetary grade on the quality of their work.
Yeah, tip isn't the right word.
But I'm looking for a single word or phrase I can use to describe this thing we are calling a zap. I think you are on to something with the idea of a thank you.
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