I have purchased a Full version and users get an "Invalid license key" error message
App version 5.0.1 or later is required. Please check on App Store or Google Play and upgrade to latest version.
I have purchased a Full version and users get an "Invalid or Expired trial code" error message
Make sure users have left Trial Code field empty in their app settings...
I get an error message asking me to check permissions when opening the app
You should first have a look at your PHP/Apache error log for more details on the error. It is likely that permissions are not correct in your custom and mobile folder, and default_permissions are not set correctly in config.php. All files in custom folder and subfolders should have the same permissions as index.php in your CRM root folder. All folders in custom folder and subfolders should have the same permissions as the modules folder. Once you have solved the issue, you should update config.php so that the problem does not happen again next time you install a new version of the server module.
You should first make sure that the apache user and group is set in config.php (default_permissions user and group).
If permissions of index.php are 775, you should define :
'dir_mode' => 509, 'file_mode' => 436,
If permissions of index.php are 755, you should define : 'dir_mode' => 493, 'file_mode' => 420,