Integrating a Verification-Number API: Endpoints, Flow, and Error Handling
2026-08-28 · SMS-GO Research Team · 8 min read
Written by the team that operates SMS-GO. Figures reflect first-hand operation and an August 2026 audit of 16 providers\u2019 published price data. Pricing moves, so treat specific numbers as a snapshot.
If you are building automation, the API is the whole product. This is the shape of a verification-number API, the standard flow from checking balance to receiving a code, and the error handling that separates a robust integration from a flaky one.
The standard endpoint set
Most verification APIs — including SMS-Activate-style ones — expose the same handful of operations.
- Balance: how much credit is available.
- Prices: per-service cost and stock.
- Get number: allocate a number for a service, returns an id.
- Get status / SMS: poll or receive the code for that id.
- Cancel / finish: release the number when done.
The happy path
Check balance, look up the price and stock for your service, request a number, wait for the code, then finish the number. Each step has an id you carry forward.
Handle the failure modes explicitly
The integration quality is in the error paths.
- Insufficient balance: stop before requesting a number.
- No stock: back off and retry, or fall back to another provider.
- No code within the window: treat as a failure, request a refund if offered, and move on.
- Duplicate delivery: deduplicate on the message id.
- Auth failure: the API key is wrong or expired — do not retry in a loop.
Webhooks beat polling at scale
Polling the status endpoint works for low volume. For pipelines, a webhook that pushes each code to your endpoint is faster and cheaper. If the provider offers both, prefer the webhook and keep polling as a fallback.
Idempotency and retries
Network failures will happen. Make your number-request idempotent where possible so a retry does not allocate a second number, and put a ceiling on retries so a dead provider does not burn your balance.
SMS-GO’s API
SMS-GO exposes REST v1 for balance, prices, and numbers, plus an SMS-Activate-compatible endpoint so clients built against that protocol can point here. Codes can be pushed to your webhook as they arrive.
Questions, answered
What endpoints does a verification API need?+
Balance, per-service prices, get-number, get-code/status, and cancel/finish. That covers the full flow.
Should I poll or use webhooks?+
Webhooks for pipelines — faster and cheaper. Polling is fine for low volume and as a fallback.
How do I avoid double-allocating numbers on retry?+
Make the request idempotent where the API supports it, and cap your retries.
What if no code arrives?+
Treat it as a failure after the window, request a refund if offered, and move to a fresh number or provider.
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