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Android SMS Gateway Troubleshooting: Duplicate sends

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Android SMS Gateway Troubleshooting: Duplicate sends. KB article diagnosing duplicate sends. Symptoms, likely causes, validation steps, recovery. Priced by devices and SMS send volume; BYO phone and operator credit.

Written by the SMS Gateway team for operators who run phones and airtime themselves — not for theoretical cloud SMS demos.

InformationAndroid SMS GatewayTroubleshootingOperations
Article
Published
August 15, 2025
Updated
August 22, 2025
Reading time
16 minute read

Key Takeaways

  • Duplicate SMS is almost never “the API randomly double-billed.” It is a retry, a replay, or two radios.
  • Stable Idempotency-Key per business event is the first fix. A new UUID per HTTP attempt is the bug.
  • Webhook retries reuse X-SmsGateway-Event-Id. Unique-constrain it before any auto-reply send.
  • Two paired devices without deviceIds can both take a job you thought was singular.
  • Duplicates consume operator airtime and platform volume. You do not get that back.

Android sms gateway troubleshooting duplicate sends is a KB, not a feature pitch. Two bubbles on a lock screen, two live OTP codes, two “table ready” texts. Find which layer minted the second job.

Design article: idempotent send. Webhooks: server webhook. Docs: Developer Center.

SMS #1SMS #2

What duplicate sends look like

  • Two GSM bubbles, same body, seconds apart.
  • OTP verifier accepts only the second code.
  • Panel shows two message ids for one order.

Timeouts are not failures until you have looked up the first message id. Blind retry is how you buy two segments.

HTTP method safety is a client problem; see RFC 9110, then still send a business-stable key.

Cause → check → fix

CauseCheckFix
HTTP retry, new keyTwo POSTs, two Idempotency-KeysKey = orderId / challengeId; lookup before second POST
Webhook echoAuto-send inside message.deliveredUnique event id; never send on DLR replay
Two devicesBoth radios online; deviceIds omittedPin OTP; do not round-robin auth
Queue worker restartBulk prefix resentPer-row keys
UI double-submitTwo clicks, two jobsDisable button; same key both clicks

HTTP retries

Load balancers retry. The sample send curl already includes Idempotency-Key. A new GUID per attempt defeats it. API.

Webhook-driven echoes

Delivery callbacks retry. If your handler “confirms” by sending another SMS, you will loop. Webhook product page.

Two phones, one job

Failover is good until both are healthy and both send. Multi-device limits. Pin OTP with deviceIds.

Double-tap and workers

Bulk: bulk SMS. Rate-limit UX so the host cannot mash “ready.” Rate limits.

Airtime you already spent

Duplicates bill the operator and the platform meter. Free: 300 SMS lifetime. Developer: 25,000/year. Starter/Pro/Business uncap platform volume, devices 2/5/15. Pause on Free/Developer at allowance. No unlimited carrier SMS. We do not cash out unused operator credit.

Pricing.

Checklist

  • One key per business event in logs next to message id.
  • Event-id unique index before auto-reply.
  • OTP pinned to one deviceId.
  • Staging: force a 504 and count bubbles — must stay one.

Next steps

Break your client on purpose. One destination thread, one bubble. Setup · downloads.

Related product pages

Jump to the live product docs for this topic—not another long-form article.

FAQ

Frequently asked questions

Direct answers about android sms gateway troubleshooting duplicate sends.

Why did my Android SMS gateway send the same SMS twice?

Most often: client timeout then retry without the same Idempotency-Key; webhook handler that sends on every delivery callback; or two devices eligible for the same POST.

How do I prove it was a retry?

Compare request ids / message ids in the panel and your logs. Two message ids ⇒ two radio jobs. One id returned twice ⇒ idempotent replay (good).

Will the operator refund the extra SMS?

No. Carrier airtime is spent when the SIM transmitted. We refund platform plan fees per policy, not operator credit.

Does this cost plan volume twice?

If two jobs hit the radio, yes. Free is 300 SMS lifetime.
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