I guess that would also apply to zaps too. As the GBP value is so small and you get a certain amount of capital gains tax allowance, it shouldn't be an issue. Unless you are zapping a huge amount 😀⚡
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But for the receiving end, in certain cases it can be handled as a tip, which in certain countries are not taxed.
Donations are not taxed (or only partially taxed) up to certain amounts in a bunch of countries.
Yeh again not sure about tips in other countries but you are required to pay income tax on tips in the UK. Good luck to hmrc tracking 21 sat zaps ⚡