After setting up VPN on your FritzBox, usually the internet does not work on the client when you’re connected to the VPN. This is a known bug in FritzOS. To fix this do the following:

  1. go to Internet -> Filter -> Listen
  2. uncheck Teredo-Filter aktiv
  3. Apply
  4. check again Teredo-Filter aktiv
  5. Apply

The internet connection should now work for the client.