Ok, after further investigation, it seems that neither the platform agnostic nor the permission.group (ie : “Location” or “android.permission-group.Location”) work properly when added as the appPermission in the options of the native.showPopup.
However, calling one of the item in a permission group (ie : “android.permission.ACCESS_FINE_LOCATION”) works properly.
The current documentation is either completely wrong, or there is a bug.
This workaround is not so convenient, as it is now necessary to request all the items of a permission group one by one instead of the agnostic group, which might be quite annoying for the user (one popup after another).
EDIT : Actually, it works to request an array of strings, so it is not really a problem.
Cheers,
Dim