> 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/prerequisites.md).

# Prerequisites

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

What you need in place before writing the first line of integration code.

## On the IDlayr side

* **An approved IDlayr project** with the `reverse_sms` scope on its OAuth2 credentials. Projects are created by your IDlayr administrator via the Enterprise Portal — see [Projects](/get-started/concepts/projects.md). Each project is approved per use case; allow time for the approval flow before going live.
* **The project's `client_id` and `client_secret`.** See [Credentials](/get-started/concepts/credentials.md).
* **Production or sandbox mode** decided. Sandbox lets you test the full flow without real SMS traffic. See [Project modes](/get-started/concepts/project-modes.md).

{% hint style="warning" %}
Reverse SMS is currently **Early Access**. Production approval and rollout are gated on a per-use-case basis. Contact your IDlayr team to discuss enablement.
{% endhint %}

## On your backend

* A way to mint OAuth2 access tokens against `POST /oauth2/token`. See [Authentication](/get-started/authentication.md).
* A way to POST `/v1/number-verification/reverse-sms-checks` over HTTPS.
* A callback endpoint (recommended) to receive the terminal-state notification, or a polling mechanism against `GET /v1/number-verification/reverse-sms-checks/{check_id}`.
* A safe place to store the `client_secret` (e.g. a secrets manager). Don't commit it to source control or environment files.

## On the device

**No IDlayr SDK is required.** The device-side step is your app opening the native SMS composer via the standard `sms:` URL scheme. This works on iOS and Android out of the box — no installation, no platform-specific permissions, no Cloudsmith entitlement.

What your app does need:

* The ability to open `sms:` URLs (`UIApplication.shared.open` on iOS, `Intent(Intent.ACTION_VIEW)` on Android).
* A reliable channel to receive the destination MSISDN, message body, and `check_id` from your backend.

## Device capability requirements

* **The device must be able to send SMS.** Tablets, e-readers, and certain data-only devices are excluded. Use [Eligibility](/products/eligibility.md) to pre-check coverage.
* **The user must tap Send.** Both iOS and Android require user confirmation for outbound SMS. Design your UX so the user understands a verification SMS is about to be sent before the composer appears.
* **Carrier**: The user's carrier must permit user-originated SMS in the relevant direction. Reverse SMS targets IDlayr-provisioned destination numbers, which are operated to maximise carrier acceptance — but corner-case carriers and regions can still refuse delivery.

## Network requirements

* No cellular data requirement. Reverse SMS works as long as the device can send SMS, regardless of data connectivity.
* **SMS coverage** for the user's carrier in the region of use.

## Optional but recommended

* A **fallback path**. Reverse SMS itself is often used as a fallback for Secure SNA; if Reverse SMS also fails, you'll want a third path (e.g. customer support escalation, document upload, biometric).
* A **"didn't send the SMS?" branch** in your UX, so users who cancel the composer don't get stuck waiting for the check to time out.


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