CurrentDate = CurrentDate();
One Day = 24 * 60 * 60;
FirstDay = BegOfDay(CurrentDate);
For I = 0 To 6 Do
Planner.CurrentRepresentationPeriods.Add(FirstDay + (I)*OneDay,
EndOfDay(FirstDay + (I)*OneDay));
I checked this Syntax Assistant topic in 8.3.10, it does not mention the mobile application client or server. Please see the picture.
The topic on the screenshot is Common objects/Planner/Planner. What's your platform version and which topic states that the planner is available in mobile applications? Could it be a typo that was fixed in a later version?