Twilio error code 30003 means your message failed to deliver because the destination was unavailable or unreachable. This error occurs if you are trying to reach an unreachable or switched-off destination handset.
You can send another message via a REST API request to the user to determine whether this error occurs again and again. You can also use the API Explorer in the console instead of a REST API request.
If the error code occurs repeatedly:
If the error prevails even after resolving all the above checklist points, try using the Fallback to Long Code feature of Messaging CoPilot because the message sent from shortcodes can cause an error if the destination user uses a wireless plan that doesn't support shortcode.
If none of the solutions work, you can open a Twilio support request after collecting three or more message SIDs from the last 24 hours in the SMS logs.
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