Additions and changes to the Twilio platform
When Twilio receives termination traffic to an inactive account, either due to the account being suspended or closed, Twilio will reply with a ‘603 Decline’ SIP Response. This will help trigger your infrastructure to failover to alternate trunks if your Twilio account is not active.
Included in the ‘603 Decline’ SIP response will be a X-Twilio-Error header referencing Error 10001: Account is not active. This will help your team to understand why your calls to Twilio are being declined so you can resolve the issue through adding funds if necessary or contacting Twilio Customer Support at email@example.com to inquire further.
See the docs for more information.