Checking that you've set it on. Inner button (next to cancel) enables it, then outer upper on to set speed. Once both the cruise icon and the cruise speed are green, along with the distance icon ( two parallel lines) becomes bold, then it is active.
You need to have set the cruise type to Speedo with arrow ( and so not reading speed from signs).I
So check that the icons are turning green.
I found it a faff at start to use it but soon ok.I
You can read the user guide, but it makes heavy work.
You'll also see mixed views on it, with posts on phantom braking, random disengagement, shut downs, and limitations due to using a single camera and no radar.
I've seen no issues and use it with the lane centre self steer on quiet monitor way and dual carriageway.
It has a fairly sharp operation - if approaching a slower car, it doesn't feature off, but keeps speed until gap is reached then brakes. But on quiet roads It is pleasant to use.