In order to troubleshoot the mywifiext Setup issues, you need to see the solutions down below which will help you to get rid of all any kind of troubles because of browser or connection etc.
Check the power LED light on your extender. If it is not lit then check all your wired connections
Check your internet service with your ISP (Internet Service Provider) for any laps in the network while setting up
See if all the spellings or numbers entered are correct and in the right order
If it is a browser issue then update your web browser or use a different browser
Make sure that the login credentials are all correctly filled in