The billing model is not an accounting detail. It decides what happens on the day something goes wrong.
Prepaid credit
You fund a balance and spend down. Cap spend with key budgets. The risk is holding unused credit with a counterparty. Size the balance to a measured pilot, not an annual fantasy.
Monthly bill / postpaid
You consume first and pay later. Useful for large negotiated volume, but needs hard limits and alerts so a runaway loop cannot invent an invoice you cannot explain.
Supesonic uses prepaid credit. Add funds in Wallet after a verified payment notification.