When a message fails, TextBay’s History shows a plain-language explanation plus Twilio’s own error code, and the code is the fastest route to the fix. These are the usual suspects, most common first.
Your Twilio account is a trial (error 21608) #
Trial accounts only deliver to phone numbers you have verified with Twilio, and they prefix every message with a trial note. Verify the recipient in the console, or upgrade the Twilio account to send freely. TextBay shows a Trial badge on the Twilio page when this applies.
Unregistered US traffic (errors 30034, 30007) #
Texting US numbers from a regular local number without the A2P 10DLC registration gets filtered by carriers: the message leaves as Sent and dies as Undelivered. The one-time fix is the brand and campaign registration; where you stand shows in the US A2P row on the Twilio page. See A2P and 10DLC. Error 30007 (filtered) can also hit registered senders whose content trips spam heuristics: vary the wording, drop link shorteners, and slow down.
Destination not enabled (error 21408) #
Twilio accounts start with only some countries enabled for SMS. Enable the destination under Messaging Geographic Permissions in the console; the error text in History links the right page.
The person opted out (error 21610) #
They replied STOP earlier, so Twilio refuses the send. TextBay puts these people on your block list automatically so later runs skip them: Handle opt-outs.
Wrong or unusable sender (errors 21212, 21606) #
The From value is not something Twilio can send from: a number not on your account, a sender name aimed at the US, or a voice-only number. Recheck the sender choice on the Twilio page; the manual sender box explains what the value you typed actually is.
Invalid recipient number (error 21211) #
The number is not a real, routable mobile number. Use international format (+15551234567), set your default country under Settings so local numbers resolve, and use the number converter on the Contacts page to fix a whole column at once.
Every failure row in History links to Twilio’s page for that exact error code, and the app’s explanation says what to do in one sentence. If you are stuck, send the code along: Support.