31203: No valid account.

Programmable Voice error 31203 indicates Twilio could not validate a usable Twilio account for the request.

• The Voice Access Token was created with API Key credentials that don't belong to the same Twilio account or subaccount referenced by the token, which is unsupported because API keys and secrets aren't shareable across main and subaccounts and the token's sub claim must scope to a specific Twilio Account SID.
• The Voice Access Token is missing required grants or fields for Voice SDKs, such as the VoiceGrant or the required outgoingApplicationSid for making outgoing calls.
• The Twilio account isn't in good standing or Voice calling is disabled on the project, which prevents Voice operations from succeeding.
• Attempting to build Access Tokens with a Restricted API Key, which Twilio does not support for Access Token creation.

• Verify the project is active and permitted to use Voice, and resolve account status issues before retrying. If your account is disabled or Voice calling has been disabled, follow the actions outlined for errors 10001 and 10005.
• Regenerate the Voice Access Token using the correct Account SID together with an API Key and Secret that belong to that same account or subaccount, and include both an identity and a VoiceGrant with the required parameters.
• If you use subaccounts, generate the API Key in the exact subaccount you scope the token to and ensure you're using the matching key and secret when signing the token.
• If the issue persists after issuing a new token, collect SDK logs and review Twilio's Voice troubleshooting steps to isolate configuration or environment problems, then retry with a fresh token.

• Voice JS SDK v1: Troubleshooting & Common Errors
• Troubleshooting Voice Calls
• Common Twilio Programmable Voice SDK Error Codes and Debugging Help