Why Client is Unable to login to the mobile app ?

Why Client is Unable to login to the mobile app ?

There are a few reasons that the client is unable to log in to the mobile app :

Mobile apps can be downloaded and installed on a device, allowing users to access the app's functions and services at any time, from anywhere. You can download no-charge and paid apps from Google Play on your Android phone and the App Store app on your iPhone or Ipad.

1. Incorrect password 
2. Invalid token Number. 
3. Incorrect Username
4. Mobile app version is not up to date.
5. Mobile does not link to the internet.

To have the maximum benefits of a mobile app user should use an "up-to-date mobile app version" with an "up-to-date version of mobile platform"