If after taping on the app’s icon you see this message you need to ensure that your phone allows installation from unknown developers before you install/upgrade the TeleMessage app. Tap Cancel and continue following this section.

Open device Settings and tap
General.

→

Tap Device Management’.

→

Tap the source of installation.
The source name might change according to your company preferred method of installation.

→

Tap Trust [‘installation source’].

    →

Tap Trust.