DNS settings are invalid.
Step 1: Restart the PlayStation 4 system to refresh the network connection.
Step 2: Go to [Settings] > [Network] > [Test Internet Connection]
Step 3: If you selected [Manual] under [IP Address Settings] or [DNS Settings] when you set the Internet connection for your PlayStation 4, make sure that the [Primary DNS] and [Secondary DNS] are set correctly.
In other cases, the system might not have obtained an IP address, or the DNS settings may have been changed.
Please contact your Internet service provider for further assistance.