At the moment the teleporter always says "Not standing on teleporter" and does not allow use.

Hello,
I cannot replicate the bug you encounter.
It might be that the activation area is some time hard to stand on (the circle in the middle of the building) or it might be that another mod changes the “turret entity” that this building uses to detect the player entity.

Can you show me the problem and also what mod list are you using?

Hey. Only mods I used were Interplanetary Teleporter and the Creative mod on a new save for testing.

I just tested it with Editor extended and it seems to work.