To resolve the issue with the NuMi app not working on your cell phone, follow these steps:

1. Check Network Connection: Ensure that your device has a stable internet connection, as the NuMi app requires internet access to function correctly.

2. Restart the App: Exit the NuMi app completely and then reopen it. This simple action can resolve many temporary glitches.

3. Clear Cache and Data:
- Go to your device's Settings.
- Select Apps or Applications Manager.
- Find and select the NuMi app.
- Tap on Storage and then choose Clear Cache. If problems persist, tap Clear Data (note that this may delete local data).

4. Update the App:
- Visit the Google Play Store and search for the NuMi app.
- If an update is available, click on Update to ensure you have the latest version of the app. Updates often contain bug fixes and improvements - learn more.

5. Device Reboot: Restart your phone to refresh the system, which can often solve minor software issues.

6. Reinstall the App:
- Uninstall the NuMi app from your device.
- Reinstall it by downloading it again from the Google Play Store.

7. Check for App Outages: Sometimes, the app itself may be experiencing issues or outages. You can check platforms like Reddit or community forums for any announcements or user discussions regarding the app's status - learn more.

8. Contact Support: If none of the above steps work, consider reaching out to Nutrisystem support for further assistance. They may have additional troubleshooting methods available - learn more.

By following these steps, you should be able to troubleshoot and hopefully resolve the issue you're experiencing with the NuMi app.