As far as I know the HTTP interface is “disabled” for all Heos-based models (with a H at the end of the model number). If you try to open the IP of the AVR in a browser and it gives you a 403 Forbidden, this is the case.
If the HTTP interface is secured, the DENON binding cannot send any commands to the receiver.
It’s still possible to receive events when putting the binding in telnet mode. Sending via telnet is not supported by the stock binding, so I made a fork (tested with an X4400H):
