SMS messages not sending — A2P, carrier filters, and content blocks

SMS not sending

When SMS stops working, the cause is almost always one of three things: A2P 10DLC registration issues, carrier content filters, or recipient-side blocks. This article walks through diagnosis in the order most likely to find your specific problem.

What "not sending" actually means

In the *Activity → SMS* feed each message has one of these statuses:

• `queued` — accepted by us, waiting for the carrier.
• `sent` — handed to the carrier, awaiting delivery confirmation.
• `delivered` — recipient's device acknowledged.
• `undelivered` — carrier rejected (filter, bad number, no SMS capability).
• `failed` — internal error before reaching the carrier.

Stuck in queued for >30 minutes means our outbound queue is backed up — rare, almost always self-resolving. Stuck in sent for >24 hours means the carrier accepted the message but never confirmed delivery, usually because the recipient's phone was off. undelivered is the one that needs investigation.

Cause 1 — A2P 10DLC registration not approved

US carriers (AT&T, T-Mobile, Verizon) require business SMS to be registered through The Campaign Registry. If your registration is pending or rejected, T-Mobile in particular will block ~95% of your messages.

Check status in *Settings → Compliance → A2P status*:

• Approved (Standard) — full throughput, no carrier blocking.
• Approved (Low Volume) — 2,000 messages/day cap on T-Mobile. Fine for most low-volume owner notifications and customer-initiated replies.
• Pending — submission in flight; can take 1–10 business days. While pending you're at Low Volume.
• Rejected — almost everything blocks. The dashboard shows the rejection reason.

The most common rejection reason is EIN mismatch — the EIN you submitted doesn't match the IRS record. Re-submit with the EIN exactly as it appears on your IRS letter. The second most common is brand name too generic ("ABC LLC" gets rejected; "ABC Plumbing of Sacramento" gets approved).

Cause 2 — Content filters

Carriers use machine-learning filters that flag messages with certain words and phrases as spam-likely. The filters are opaque and change frequently, but the patterns are stable:

• Money words: "free," "winner," "cash," "discount," "save 50%."
• Urgency words: "act now," "limited time," "expires today."
• Click-through words: "click here," "tap here," "go to."
• Adult-content words: anything that could be construed as 18+ content gets blocked even in legitimate contexts.

If your message template includes any of these and you've recently started seeing high undelivered rates, that's almost certainly the cause. Edit the template to use plain language ("$10 off your next visit" instead of "free $10 with this offer") and resend.

Cause 3 — Recipient-side blocks

Two things can block on the recipient side:

• The recipient texted STOP. Once a recipient replies STOP, we permanently block sending to that number — this is a hard TCPA/CTIA requirement, not optional. The Activity feed shows the inbound STOP message and the date. If they want messages again, they need to text START.
• The recipient's number is a landline or non-SMS VoIP. Some VoIP services (notably some Vonage and RingCentral lines) don't accept SMS at all. The carrier marks these undelivered with a reason of "not SMS capable."

Look at the undelivered row in *Activity → SMS* — the reason is shown explicitly.

Cause 4 — From-number reputation

If your BizRnR number has been used to send messages flagged as spam in the past (rare, but happens with shared pools or recycled numbers), T-Mobile's filter may downgrade its reputation. Symptoms: messages send fine to AT&T and Verizon but consistently undelivered to T-Mobile.

Fix: open a ticket with support@bizrnr.com and request a number replacement. We'll provision a fresh number with no history; takes about 10 minutes. Your existing forwarding stays, your inbound calls keep working, and SMS reputation resets.

Cause 5 — Outbound campaign attempted without approval

Cold or marketing outbound SMS requires an enabled campaign workflow, documented consent, sender registration, opt-out handling, and policy acceptance. If you are trying to send a campaign from an account that has not been approved for outbound, the platform refuses the messages.

What to do when nothing else works

Email support@bizrnr.com with one specific message ID from a recent failure (visible in *Activity → SMS*). We'll pull the full Twilio error code, the carrier-side response, and tell you exactly what blocked. Most cases get diagnosed in under an hour.