Do they go grocery shopping? Get cash back when paying with debit. It's free and handy.
> no one wants to have to harass their friends about money.
Sounds like more of a personality issue... clearly they have the means to pay if clicking a button works. Back in the dark ages my roommates and I just kept a running tally of who owes what on the whiteboard. Kinda nice because you can use those amounts as "accounts" -- I owe you $20 for internet, but 4 days later you owe me $20 for dinner, so we're square. No need for a transaction at all. We'd settle up, if need be, at the end of the month by writing checks. These days you don't even have to go to the bank to deposit them.
> With the bill split app, the person who pays racks up reward points on their credit card
...and then pays 4%. Worth it?