This will be due to your TV being only HD, but your home theatre being 4k pass-through capable. The home theatre is handshaking 4k, then passing 4k video to your TV, which doesn't know what to do with it (not compatiable).
Plug the STB into the TV direct and force (save) it to 1080p. Then, plug it back into the home theatre.
This should resolve the issue.
I work in Media Operations.
Please note that I am not a part of the social media team and help out on my own time where possible.
Managed to change it to 1080p and all looked promising until routed back thru the receiver and same error “the content cannot be displayed. To display, please connect with the HDMI Input which supports HDCP 2.2 on the TV”