> For the complete documentation index, see [llms.txt](https://docs.idlayr.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.idlayr.com/products/number-verification/reverse-sms/testing.md).

# Testing in sandbox

{% hint style="info" %}
**Backend API** · Early Access
{% endhint %}

Test Reverse SMS without real SMS traffic by using a sandbox project. The last digits of the `phone_number` drive the simulated outcome — no real outbound SMS is sent, no real carrier billing.

See [Project modes](/get-started/concepts/project-modes.md) for the general sandbox model.

## How sandbox testing works

In sandbox mode, IDlayr returns simulated SMS routing details on the create response and simulates the carrier-side verification once the device-side step "happens". The shape of the response is the same as production — your integration code doesn't need to branch on environment.

Your app still opens the SMS composer (or you skip that step in automated tests) — the sandbox doesn't require an SMS to actually leave the device. The simulated outcome is driven by the MSISDN suffix on the create call.

## MSISDN suffix map

| MSISDN ends with                     | `match` | `status`    |
| ------------------------------------ | ------- | ----------- |
| Even digit (`0`, `2`, `4`, `6`, `8`) | `true`  | `COMPLETED` |
| Odd digit (`1`, `3`, `5`, `7`, `9`)  | `false` | `COMPLETED` |
| `00`, `55`, `99`                     | —       | `ERROR`     |

For the cross-product overview of sandbox — what's simulated, what isn't, sandbox retention — see [Sandbox testing](/get-started/sandbox-testing.md).

## Testing without sending an SMS

Because Reverse SMS doesn't use an SDK, sandbox testing is straightforward:

* **Backend-only tests** — call `POST /v1/number-verification/reverse-sms-checks` with a sandbox MSISDN, then poll or wait for the simulated callback. No device involved.
* **End-to-end tests with the composer step** — run the full app flow on a simulator or emulator; the `sms:` URL opens the composer, but you don't have to send anything in sandbox mode. The check still resolves based on the create-time MSISDN.

## What sandbox doesn't simulate

* Carrier-side SMS delivery delays and timing variation.
* Country-specific SMS pricing or regulatory restrictions.
* User cancellation of the SMS composer in real-world conditions.

Run a small set of production checks against real numbers in your target markets before going live, particularly to validate carrier coverage for user-originated SMS.


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