Try this step:
Go to your [Vapi billing page](
https://dashboard.vapi.ai/org/billing) and look for the option to
"Switch to Credit Based Billing." Click it if available, then attempt your purchase again.
If the issue persists, double-check that your payment method is saved correctly, or try re-adding it.
This step is recommended in the Vapi support documentation for similar credit purchase issues.
Source:
- [Vapi Changelog](
https://docs.vapi.ai/changelog/2024/10/10)