> ## Documentation Index
> Fetch the complete documentation index at: https://moengage-doc-2312-standard-user-attributes.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Why Do Push Notification Tests Often Fail for Mobile Numbers?

> Resolve push notification test failures when using mobile numbers by switching to the unique user ID field to identify reachable users instead.

## Problem

When attempting to send a test push notification campaign, the notification fails, and the following message is displayed:

Installed User not found for Mobile Number = 0000000000

<img src="https://mintcdn.com/moengage-doc-2312-standard-user-attributes/aIDxo_nsCMfuJa4e/images/moengage_06d833.png?fit=max&auto=format&n=aIDxo_nsCMfuJa4e&q=85&s=8bece250a36797c7510cceaec6a2f79d" width="556" height="304" data-path="images/moengage_06d833.png" />

## Solution

* Use the unique ID field of reachable user instead of the Mobile Number attribute to ensure push notifications are sent.
* The unique ID field can be found in the user profile with the name **ID**.
  <img src="https://mintcdn.com/moengage-doc-2312-standard-user-attributes/A8U5WsLqYnHBTzTw/images/moengage_93aff4.png?fit=max&auto=format&n=A8U5WsLqYnHBTzTw&q=85&s=6604f9ef0f5de981f5c2a3d1a293c0c6" width="1600" height="275" data-path="images/moengage_93aff4.png" />
* The unique ID is unique to each user and is used to determine whether the user can receive push notifications.​​