Hi,
Have you made sure that when it told you to enter Device ID - you've entered a serial number of your router?
If yes, it could be other issues like:
1. Check your internet connection, can you ping 8.8.8.8 from the routers CLI?
2. When configuring Cumulocity did you write the server address? It must the address that is in your Cumulocity profile url.
3. Have you updated your router to the latest firmware version?
EB.