I REALLY need some expert help here. I acquired a P4 used. It didn't have a controller, so I purchased a second hand GL300F, which the DJI compatibility chart says will work. I can't get the two to link up. I check the firmware in DJI GO4 and it automatically loads the P4 Pro profile. I try to downgrade the firmware or change it and DJI GO4 says it has no firmware for a P4 standard. I'm confused, frustrated, and about to start breaking things. Any ideas?? Thanks in advance.