This is the solution for p4:
1) Install DJI GO App from Apps store, launch app (not the GO 4 app)
2) Select P3 Pro as aircraft , using the 3 dashes at the top right of the app press and hold for 10s or so. A new screen appears showing suggested current firmware of RC. Scroll down to firmware 1.6.0 select "Firmware Refresh". Wait for it to install then close the app and shut off RC.
3) Reboot RC, after a new minutes on shut off RC
4) Open up DJI GO, Select P3 Pro and press camera (have the lightning cable connected to RC and iPad/iPhone).
5) Once in main screen with telemetry info wait a few minutes and press the Left upper area just next to the DJI logo saying "No xxxxxx connected " in red, this will take you to the Aircraft setup screen.
6) There you will see a warning message triangle, press this area and it suggests upgrading the firmware as you have 1.6.0 installed and the latest is 1.9.3
7) This started the firmware download and then with lots of beeps and blue flashing light the upgrade was a success.
8) On completion it will tell you to reboot the RC. At the same time I closed off the DJ GO App.
9) Reboot the RC again.
10) Turned on P4 and launched DJI GO 4 App.