Hi Carlooo,
Thanks — we can help. If your balance is negative (e.g., -$0.01) the dashboard sometimes requires you to re-save a payment method before purchases succeed. Please try this:
1. Open dashboard.vapi.ai → Settings → Billing → Payment methods.
2. Add or re-enter your card, then click the grey checkmark to save (you should see a toast and the card numbers become masked).
3. After the card is saved, try buying credits again.