Don’t panic, the tow bar is not faulty, it means when you took it off the release mechanism wasn’t turned far enough around to click it into the open position.

In this situation the neck simply springs back into the locked position when its off from the car.

So when you go to attach again its in this locked position and it won’t clip back on.

To resolve this you will first need to put it back to its unlocked position.

Here is a video from witter that shows what to do