Soap-
There are a couple of things people have reported worked when a setup fails to complete.
Easiest to try, so try this first: Restart your router, even if other devices have no trouble connecting. When your router has completed its startup, try repeating your Roku setup.
More involved: Repeat the setup by connecting to a different wifi network - perhaps via a wifi hotspot on your mobile phone or by taking it to a friend's house - and see if it will complete the startup. If successful, then redo the wifi connection to use your intended home wifi network via Settings > Network > Set up connection.