Thanks for the feedback! Will add this in the next update (1.29.0 on Android), forgot to add it earlier.
Once you have the update, go to an entertainment program (like Sync), and tap the button to select entertainment areas. There you will see a list of groups. Then tap the three dots of a group, where you will see a Details button. Tap it and there is the identifier of the group. The identifier could be a bit long, but you can long press it to copy it to clipboard.
The identifier of a bridge can be found by going to the Devices tab, select your bridge, and tap Details.
I expect the update to be available within a few weeks. Unfortunately there is no workaround to get the identifier without this update.