Do_Mount_Control Param's Not Saving

Hello. New here.

I am having a problem auto tilting the gimbal after a waypoint. I use DO_MOUNT_CONTROL and add ‘90’ to the pitch. When saving to disk the parameters save. When written to the drone the parameters are setback to ‘0’.
I am using MP 1.3.37 and the model of my drone is Walkera Tali H500. Am I missing something? My gimbal works fine from the radio.