There was a public WIFI with no password protection. Everone could connect to the WIFI, but there was no internet access, even tough they promoted it at the entrance of the restaurant. No employee was able to support, so I decided to connect to the router and try the standard login credentials. Usually they are user:admin pw:admin or blank password. This worked and I was able to restart the router. After the restart, the router could connect to the internet and everyone could access the web again.