hdcp

Try restarting the Apple TV, if that does not work, then unplug it for 2-3 minutes (from the back of ATV) and the plug it back in and re-attempt. High quality HDMI cables make a big difference.

I also found this article, please read it and maybe it will help.

https://support.wbfyc.com/kb/article/86-apple-tv-4th-gen-hdcp-error/

By the way, locked down in California so I feel your pain.

You may not be using a high quality cable, please use one similar in quality to:

https://www.bestbuy.com/site/rocketfish-4-4k-ultrahd-hdr-in-wall-rated-hdmi-cable-black/3720002.p?skuId=3720002

Please describe the issue in detail and what error messages you are getting so we are not guessing.

Glad it worked okay and the device is working okay again.