How to add a device to a group

I’ve added group #2 to some of my light devices (ZRP200 & ZDP200). However, when I tap the right button om the ZRM230 the light does’nt turn on.
When I check the group associated to the device through the “view” button it seems that non of the devices is associated to the group (yes, I tap the save button first…)
Who know a solution?