I got good service from DJI with a replacement Mini 4K
It would not pair with the app and have tried the DJI assistant all firmware is up to date. I did try to remove the old Mini 4K to see if that was a problem. now I’m wondering what i might have done to make things worse for myself.. in device management of the Fly app
i have this.. shouldn’t the RC be in the listing?
Well I have it sorted at last..
There are a few options to try from DDJI advice and others.. none worked till I saw this video
https://youtu.be/7ZW3ZeP_eXs?t=297.. should start at 4:57 into the video
TLDR.. link the RC to the Drone without the phone/app running. paired in a few seconds!!!
it’s up and running now… Might help someone else.
PS i noticed a few on the DJI forums trying the same procedure as i had been.. to no avail. I left my experiences on that too
These things make me smile 
Video title:
How To Quickly Bind Your DJI Drone and Controller
Real world advice:
Interesting, but did you try this
.
Linking the Remote Controller
The remote controller is linked to the aircraft before delivery. Linking is only required when using a new
remote controller for the first time. Follow these steps to link a new remote controller:
1. Power on the remote controller and the aircraft.
2. Launch DJI Fly.
3. In camera view, tap and select Control and Pair to Aircraft (Link). The remote controller will beep
continually.
4. Press and hold the power button of the aircraft for more than four seconds. The aircraft beeps once
to indicate it is ready to link. The aircraft beeps twice to indicate linking is successful. The battery
level LEDs of the remote controller will glow solid.
Make sure the remote controller is within 0.5 m of the aircraft during linking.
The remote controller will automatically unlink from an aircraft if a new remote controller is linked to
the same aircraft.
Glad you finally managed to get it sorted. Would have thought DJI would have sent some sort of instructions with the replacement advising you would need to do this
They have given lots of help but nothing worked. The drone never beeped holding the power button down..
It only did that when phone not attached to the RC .
After that it was seconds to linking 
Yes tried that.. Section 4 never happened for me
That caught me out a few weeks ago, I’d been using a smart controller, but when I went to a Beacon park meet I forgot to put it in the car, oh well I thought I’ll use the original controller (that is always in my bag) but wouldn’t connect, it took @stevesb to sort it out, I’d never even considered it needed re-pairing..
