That sounds like a server error, not able to find the content.
Maybe try uninstalling Netflix and installing it again on the Apple TV.
click here ➜ Install or delete apps on Apple TV - Apple Support
You may also want to contact your Internet service provider and verify they aren't blocking Netflix for some reason. Unlikely, but it can happen.
Also, just to rule out potential causes, you may want to take your Apple TV to a friend or relative's house and test it out on their internet connection and see if it works.
If Netflix works there, but not at home, the it may be an issue with your internet connection, or your ISP as mentioned blocking Netflix specifically.
If it does not work, then it's possibly an issue with the App or the Netflix service directly.
If other services on the Apple TV are working correctly, it's unlikely to be an issue with the Apple TV itself, so changing it out will probably not resolve the issue if its caused by something external.