Drachensilber

Make sure you enter the activation code properly (double click the code you've entered).
The activation code will expire within a certain time period. Hence use it until it expires.
The activation code may only be used once, and can't be used for more than 1 device.
If you discover the code is not working, then get a new one with the assistance of the alternatives available in your Roku remoteroku.com/link
See if your internet connection has some issues. If yes, fix it immediately.
For those who have a wired internet connection, then ensure that the LAN or Ethernet cable is connected properly.
Contact your ISP to see whether the matter is really on their side.