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. 


>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.


windward

This is a pretty accurate description but doesn't really roll off the tongue. 

But it reminds me of throwing some money in a street musician's hat and I like that image more than tipping a driver or Batista. The former is a gift, while the latter is a fee. 