Can't add Onkyo TX-RZ820 to Google Home

[TraxtarXKR]

I can't add my Onkyo TX-RZ820 receiver to my Google home. 

It shows up in the list of devices, but when I try to add it to a room, it gives an error: 

"This Google Cast speaker is connected to another account or home"

There are no other homes on my network, or other accounts registered.

I can mirror audio from my device to the receiver via Chromecast, so it's definitely on the correct network and can be access by other Chromecast enabled host devices.

In the Onkyo controller app, I can see the Chromecast version of the receiver. 

I called Google support, and they were not helpful. Basically recommended I factory reset the receiver (that didn't solve it), and reinstall the Home app on my device.

Any ideas on how to resolve this?

[TraxtarXKR]

To add, I cannot see the receiver in player apps like Pandora or SoundCloud, because the device isn't added to the home. It just shows up under "Local Devices" for mirroring audio.