Partner accounts in PromptForm rely on wallet balances to consume and charge for API usage. That wallet balance is also used by any sub-user or end-user under the same account.
When the wallet balance reaches a certain threshold amount configured in the partner account profile page, the wallet is automatically topped up to the preferred amount.
The payment method on file is used for the wallet balance top-up.
If the wallet ever reaches negative balance from API usage, the card on file will be auto-charged immediately to cover the negative balance, regardless of the auto top-up setting in the PromptForm account.