RAK 811 Multicast

Good Day,

I have RAK811 nodes and RAK7249 outdoor gateway, connected with local Chirpstack LoRaWAN server.
I would like to use Multicast group option in the server to send a down-link message from the server to all the nodes in the group.
I have set up every thing in the server and added the nodes. The nodes joining using OTAA and it’s class C.
I configured the nodes with dev_eui, app_eui, app_key for OTAA join method, and dev_addr, apps_key, nwks_key to use multicast group.
I can send downlink one by one to each node, but I’m still not able to use the multicast.
Is there a special configuration in the nodes?! does RAK811 support multicast?

Any help will be appreciated !

I am very sorry that the current node does not have the broadcast mode on, so it cannot receive the downlink data at the same time.