Reading the manual at Pages 59-60, where the airplane door configuration is explained would be a good start to know what the issue might be. In case the airplane uses custom variables to control doors, you will have to set a custom XML expression to check their state, so the relevant paragraph in the manual would be in this case the "Airplane using Custom Variables for doors" at Page 60.
Of course, the next step would be knowing which variables are assigned to each door, so it might be probably easier to ask the developers.
Also, I see there is an official GSX profile here:
https://wiki.prosim-ar.com/index.php/Visual_Flight_Model#Ground_Services_XIt's seems to be included in the P3D version but, chances are the variables haven't changed, so you might just have a look at it, and copy the XML expression to your configuration. If the visual model is the same (same reference point and sizes), I guess you can just use the profile as it is.