bt_mesh_model_send relayable?

Hello, 

I am looking into relay nodes and my nodes do not seem to relay,

All nodes are provisioned with the same provisioner and have the same keys 

The following configs are enabled - 

CONFIG_BT_MESH_RELAY=y
CONFIG_BT_MESH_RELAY_ENABLED=y
CONFIG_BT_MESH_RELAY_RETRANSMIT_COUNT=5


The messages that are sent are vendor model messages using:
bt_mesh_model_send sent to BT_MESH_ADDR_ALL_NODES. 

bt_mesh_model_send does not have any acknowledgement, am I correct in saying bt_mesh_model_send cannot be relayed? and if not any pointers what to look for in this issue
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