A prepaid balance is credit deposited in advance and debited per message as traffic is sent; it replaces invoices, cards on file and credit lines, and it is what a crypto-funded gateway runs on.
Prepaid is the natural model for crypto payments: a deposit is confirmed on its network, converted at the market rate, and held as a USD balance that each message draws from. There is no bill at the end of the month and no exposure for either side. The balance shows what is left and what a campaign will cost before it is sent.
The practical points: keep the balance ahead of planned campaigns, set a low-balance alert, and know the refund rule for what is unused.
At SMSMeteor: the balance is in USD, never expires, is checked before a campaign is queued, and triggers a balance.low webhook under your threshold. Unused balance is refundable under the refund policy.