Yeah, I can imagine it would be tough to charge for this, especially on a recurring basis. If I was splitting a bill, and thought I could use this, but then it turns out I'm going to have to pay $5 or a monthly subscription or something, at that point I'd probably just split the bill manually.

If you actually handled the payments, you could introduce a small upcharge that way, but even there it might be a hard sell, and the amount of bullshit you'd have to deal with to be able to scrape a buck or two off each transaction might mean the juice isn't worth the squeeze. But still, if you could scale it enough, a buck or two per transaction could be big money!