1. Switch ON your Zappiti 4K HDR.
2. Click on SETTINGS button.
3. Click on Developer options button.
4. In Color space mode, please select Y'CbCr 4:2:0 option.
As the HDMI 1.4 support up to 8.16 Gbps total bitrate, the 4K resolution will be fully supported in Y'CbCr 4:2:0, even in 10-Bit. But if you do not get any picture, please set the Zappiti player in 8-Bit ( Developer options / Deep Color mode).
If your AV Receiver is only compatible with HDMI 1.3, you will be not abble to get 4K resolutions. So, in this case, please follow this procedure to use Force SD Audio convertion over SPDIF:
[Audio] Force SD Audio for SPDIF to convert HD Audio to SD...