You can access your billing settings at
dashboard.vapi.ai/billing
Setting a Monthly Billing Limit
In your billing settings you can set a monthly billing limit:
Exceeding Billing Limits
Once you have used all of your starter credits, or exceeded your set monthly usage limit, you will start seeing errors in your dashboard & via the API mentioningBilling Limits Exceeded
.

Once you have gone over on your monthly billing limits, the API & dashboard will throw billing-related errors.