Developer not approved

You must approve “The App Lab” developer on your device to use your app:

iOS devices:

From your device Settings: 
Go in General > Device Management* > The App Lab > Add as a trusted app 

* (The name may differ, but the terms are usually along the lines of Profiles, Profiles and accessories, or Device management.)

Android Devices:

Step 1 : Click on the Settings button on your device.

Step 2 : In General, click Security and then Device Management.

Step 3 : Select Unknown sources. A message will appear: By pressing OK, you acknowledge that you are solely responsible for any damage to your device. Click OK.