SIP 402 and 503 "Payment Required" Error Codes on Voice Calls

Objective

When making outbound voice calls using SIP Trunking, Programmable SIP, or the Voice API, calls fail and your SIP logs show one of the following responses:

• 402 Payment Required

• SIP/2.0 503 Service Unavailable 4 Payment Required

Applies To

• Voice API
• SIP Trunking
• Programmable SIP

Procedure

Both error codes indicate that your Vonage account does not have sufficient balance or has reached its credit limit to process the call.

• 402 Payment Required — This code may appear in your call detail records (CDRs) or Voice API logs to indicate that the call was rejected due to a payment issue at the account level.

• 503 Service Unavailable 4 Payment Required — This is the SIP response your endpoint receives directly from the Vonage platform when a call attempt is rejected because the account balance is zero or the credit limit has been exceeded.

Although the two codes appear in different places, they share the same root cause: insufficient account funds.

1. Check your account balance

   Log in to your Vonage API Dashboard and navigate to Billing to review your current balance and credit limit.

2. Top up your account

   If your balance is zero or negative, add funds to your account. For instructions, refer to:

   1. How do I add credit to my account?

   2. How do I set up automatic payments?

3. Set up low balance alerts

   To avoid future interruptions, configure a low balance notification in your Dashboard under Settings > Notifications. This will alert you before your balance runs out.

4. Retest your calls

   Once your balance has been topped up, retry your calls. They should complete successfully.

Additional Information

If your account balance appears sufficient but you are still receiving these errors, please contact Vonage Support and provide the following details to assist with investigation:

• API Key

• From and To numbers

• Timestamp of the failed call

• Call UUID (if available) — see What is a Call UUID?