As shown in the picture, there is a clip-type closure on the side of the rack. But there is also a hole to install a lock.
We will use a standard cylinder (not included in the packaging!) without the need for further elaboration:
All you have to do is remove the semitransparent cover from the hole and insert the cylinder that we also have on the Visiotech website, named RACK-LOCK:
The final result would be the following: