It seems the domain fritz.box has been suspended. March 5 was the first time this message got captured on archive.org[1]:
The Domain Name you have entered is not available. It has been taken down as a result of dispute resolution proceedings pursuant to the Uniform Rapid Suspension System (URS).
The fritz.box name servers also point to URS[2] name servers:
Name Server: ursns1.viagenie.ca
Name Server: ursns2.viagenie.ca