When you go to Remote Controller Linking on GL300K, hit linking, hit OK  for Confrim frequency, nothing happen, no count down & no beeping,  goes back to linking screen.
Version V0.4.4.2
App 4.3.1.4

Reloaded RC Firmware, by downloading P4 Pro V2.0 to sd, said it loaded ok, But the problem was not fixed, but it still had the same problem, would not start the linking process.

Hi there. Thank you for reaching out and we're sorry for the trouble. Can you please try to download the DJI Assistant 2 software on your PC and update/refresh the firmware of the aircraft as you already updated the RC to the latest firmware, after that try to link and check if the issue persists? Kindly please perform the manual linking using the combination buttons to see if there are any changes. You may refer to the tutorial link below for your reference. Please keep us posted. Thank you.

I have already did all that, I open a case and shipped RC to your repair shop.