Twilio says "sent" but the SMS never arrived? 30007, 30034, and don't retry

Twilio returned queued. Your code logged the SMS as sent. The customer never got it. In A2P messaging, accepted is not delivered — and the codes that explain why have some dangerous look-alikes.

Queued/201 is not delivery

The send API returning queued (or a 201) only means Twilio accepted the message. The carrier can still silently filter it downstream. You must poll the status callback for the final status — delivered vs undelivered/failed — and read the error code. [tag: false-success]

The compliance failures: 30007, 30034, 30035 — don't retry

• 30007 (message filtered): the carrier blocked it as spam/policy — final status 'undelivered.' Retrying the identical message from the same number fails identically. Fix the content (remove spam-trigger words/links) or sender reputation.
• 30034 (unregistered 10DLC): the +1 number isn't on an approved A2P 10DLC Brand + Campaign (mandatory since Sep 2023). It's NOT an auth error despite looking like one. Register the number — retrying before that just burns billed messages.
• 30035 (still provisioning): wait up to 24h for carrier review, then send.

The dangerous look-alikes: 30003 vs 30006

30003 (unreachable handset) is often TRANSIENT — retry with backoff. 30006 (landline / unreachable carrier) is PERMANENT — never retry, mark the number invalid. They look similar and the base model treats them the same; the fixes are opposite. And 21610 (recipient unsubscribed) must NEVER be re-sent — that's a legal opt-out.

Snapback's messaging-a2p family maps every code to the right action — diagnose_infra_error tells you retry vs register vs never-send.