Hello,
The mobile phone must be connected to the WiFi of the router which you want to access, and the same credentials should be used to connect to RutOS mobile application (username: admin, password: your router password). Check if the app is up to date as well (current version 1.0.4). There were reports about specific mobile devices having connection issues, this should be fixed with the upcoming updates. Also, some people found a temporary solution by using a shorter password.
Best Regards,
Tomas M.