StillOwe
Split something you paid for.
You get one link to paste in the group chat. StillOwe does the asking after that, so you never have to bring it up twice.
StillOwe sends at most four reminders for a share — around day 3, 7, 14 and 30 — and they get further apart, never closer. Anyone can stop theirs in one tap, and saying an amount is wrong stops them immediately and for good.