I use https://github.com/spliit-app/spliit
It’s not the easiest to self host, as you need to know how to build docker images etc, since none is provided, but it’s more or less a splitwise substitute straight up
Caveats: its completely auth-less, so easy for people to cheat if that would be an issue for some reason. But you also dont have to force anyone to create an account
Def didnt!