WHAT A NIGHTMARE !!!!
Can't believe I am 1st one on the forum with the problem, but search did not find anything.
So, when connecting brake controller was a child play on this vehicle, once I had trailer connected, the computer start asking me the question about trailer.
Then it told me to wait till the rear camera will recognize TARGET.
WTF is the target ?????
Manual did not explain it clearly neither, when the included picture was not recognizable.
Finally some google help show, that Land Rover is using a sticker, with 3 big dots, who needs to be attached to trailer, making it the target.
I was able to find the target on ebay and finely was using the trailer today, having time to deal with calibration.
So the target needs to be attached at min 3 ft level. I have flatbed trailer, who is about 18" tall. DARN IT.
Fortunately I have mounted tool box on front of the trailer, who meets the requirement (barely).
Tool box has lock right on the center, but target glued slightly on the site is still in the view square.
So started on my driveway.
It takes about 6 button pushes to request the calibration, but the camera DID NOT SEE THE TARGET.
Here in Las Vegas we have very strong sun exposure, what blinds lot of cameras, so I drove in the shade.
Finally the camera recognized the target and the menu prompted me to drive for calibration.
As soon as i moved, the message "target lost" come again.
few more button pushed again, under next tree and camera see the target again, but as soon as I moved, the lost target message come again.
I let the play repeat about 20 times and finally gave up.
So having 25 miles drive, I just let it figure it out. Seems having sun from the side makes camera see better and few times I went into actual calibration.
Strange I could drive 2 miles with calibration showing 0 on progress bar and when I stop at red light, the calibration shoot to about 40%.
But after a minute at red light, as soon as I start moving again, the calibration bar went to 0 and whole circus starts again.
So 25 miles drive on city main streets (mostly 45 mph zones) and the computer still was not able to calibrate the trailer.
The best I got was 66%, but not for long.
See you in the future.

 

All my trailers are flat also. I gave up on it. I thought about fabricating a plate mounted at proper height, then I came to my senses LOL. I just hit no trailer attached.

 

I gave up too - Airstream trailer has gas bottles on the front that are too close to camera and it cannot focus :-(

 

What I don't know is ... if I succeed the calibration, will the car remember the trailer and I can remove the target, or do I have to keep the target?
Per my understanding the feature might be useful by estimating trailer route on backing up.
I had trailer calibration on my 2017 Ford F350 and by entering the trailer length, the blind spot assistance would cover trailer as well.
But Land Rover made the calibration well overengineered.
I rember the tow assist was $2500 option at the time, so don't want it to go to waste.