I'm pretty impressed by your efforts here. I like how you're hacking your way to solutions that work despite the rough edges (maybe more than edges) of lightning.

I was just talking last night with some people who are bartenders and they were describing a problem where someone hosting an event at a bar will pay the bar to cover an open bar, but the bar then doesn't pay the bartenders very much, thinking tip jars will cover it. But because most people pay with cards these days, they don't have the excuse of a CC transaction to add on a tip. Your QR codes solve this problem beautifully!