Key Takeaways
- A growing send queue is usually the phone: sleep, signal, empty prepaid, or OEM rate ceilings — not a missing JSON field.
- Accepted in the control plane still waits for a radio burst. DLR pending is not “API down.”
- After an outage, pace catch-up. A dump empties airtime and looks like a spam blast.
- Isolate OTP so a CSV backlog cannot starve authentication.
- Spare charged devices beat a deeper queue. Starter’s 2 devices are the usual OTP pair — dual SIM is one chassis.
android sms gateway troubleshooting queue backlog is almost never “add another POST.” It is jobs waiting on a modem. Product: how the gateway works. Live fields: Developer Center.
You bring the phone and airtime. Devices and send volume. Related: outage runbook.
Accepted · not transmitted
The bar grows while the SIM is polite and asleep.
API queue vs radio queue
Control plane accept ≠ SMSC submit. Watch pairing, device online %, queue depth, and a staff inbox canary — not only HTTP 200. DLR. App uptime.
If depth only falls when you pick up the phone, you do not have an API incident. You have a drawer incident.
Cause table
| Symptom | Likely cause | Fast check | Fix |
|---|---|---|---|
| Depth climbs overnight | OEM / battery | Exemptions, autostart | OEM restrictions |
| Paired, nothing leaves | Empty prepaid / SMS pack | Operator wallet | Top-up; two-ledger budget |
| Slow drip all day | One radio vs CSV volume | Device count vs list size | More phones, not hope |
| OTP late during campaign | Shared pool | Which SIM sent last promo | Split lanes |
Do not dump the backlog
After generator cuts or Doze, drain with a rate you already canaried. Concatenated Unicode multiplies parts. CSV. Raising OEM SMS rate ceilings is not unlimited carrier send. Load test carefully.
OTP must not sit behind promo
Separate devices. OTP. Messaging practices. STOP still applies on promo catch-up. STOP.
Fix order
1) Is the phone actually sending a canary? 2) Airtime? 3) OEM? 4) Platform allowance? 5) Then integration. Real handsets. Dual SIM is not a second queue worker.
Next steps
Canary, name the bottleneck (radio vs plan), add a funded spare if the window matters. Install the app. Spend 300 lifetime SMS proving drain rate before the next CSV.
Related product pages
Jump to the live product docs for this topic—not another long-form article.
- SMS API documentationLive endpoint reference
- device and SMS volume pricingPlans and allowances
- Android SMS gateway product guideDefinition, product, and how to buy
- download the Android gateway appGet the APK
