Questions, for people who've actually done this:
Have you let an agent spend money, or nearly, in the last few months? What was bought, and how did payment work?
What do you use to limit it (provider hard caps, a particular card, something you built)? What does it miss?
Did anything go wrong, or did you give up on a task because of payment?
Disclosure: I'm Tom, based in Australia. I'm exploring whether a service in this area is worth building. It's early research. I have no product, customers, partners or security claims to show, and I'm not selling anything. If you're willing to chat for 15 minutes about what you've actually done, reply here and I'll message back; I'll keep notes anonymous.