Hi, I hope you're doing well!
Group addresses work for passing messages to multiple endpoints or nodes grouped together in a single 16-bit address. For this, a node must have a Group Address table containing information about the groups to which each endpoint in the device belongs to.
Could you please check that the Group Address table is being generated successfully? To add an endpoint to a group, the zps_eAplZdoGroupEndpointAdd function is used on the local node.
For reference, could you please take a look at the ZigBee 3.0 Stack User's Guide, here?
Please let me know if you need any more information.
Best regards,
Sebastian