Westfalia tow bar fitting issue

[Horrgakx]

Here are 2 photos and 1 video ...

From the video you'll see it will insert but not lock.
From the photos you'll see the knob doesn't drop into the locked position.
Initially it looked like the knob was getting caught on the bumper trim, it's tight, but there's a millimetre or so gap so it will be able to rotate.

https://youtu.be/kqEewI3ETEA