21204: Call already initiated

This error indicates that Twilio has already accepted the outbound call initiation request. Create the call once with the Calls resource, then use the returned Call SID to track call progress or update the active call instead of trying to initiate the same call again.

• A duplicate outbound call request was sent after Twilio had already started the call lifecycle for the original request. Twilio can send call progress events such as initiated, ringing, answered, and completed, which means the original call may already be moving through normal execution.
• Your application attempted to manage an existing call by creating it again instead of updating the active call with its Call SID. Twilio supports updating active calls and accepts only canceled or completed as status values for a call update.
• Your application did not persist or reuse the Call SID from the original create request or status callback, so a later step retried call creation instead of tracking or modifying the existing call. (help.twilio.com)

• Store the Call SID as soon as Twilio creates the call. Use that SID to retrieve the call record or update the active call instead of sending another create request. (help.twilio.com)
• Add StatusCallback and StatusCallbackEvent to your outbound call request so your application can track when the call moves to initiated, ringing, answered, or completed.
• If you need to change a live call, update the existing call with new TwiML or a new url. If you need to stop the call, update the call status to canceled or completed instead of creating a second outbound call.
• Review the Voice logs and Request Inspector for the affected request to confirm whether Twilio already created the original call. If this error continues after you remove duplicate call creation attempts, contact support with the request timestamp and Call SID details.

• Call resource
• Make outbound phone calls
• Troubleshooting Voice Calls