Question about Denon DRA-800H

I have the device relatively new and am actually very satisfied. Now I've bought a new pair of BT headphones and I can't register them on the device. I have already read everything that has been written about this, but I have the problem that the "Bluetooth transmitter" entry in the device menu and in the app is only highlighted and cannot be selected via the device menu. Although I can access the entry via the app, I cannot switch to transmit because this entry is also darkened. Without the send function, my headphones are not recognised by the receiver. Who can help me here and has an idea? Many thanks in advance