Verify all information when adding the device are correct (Serial Num, LAN MAC, and password).
Go to System → Maintenance → Troubleshoot. Verify Internet connectivity by pinging any DNS IP (i.e. 8.8.8.8).
Access WebUI → Services → Cloud Solutions. Disable Connection Type, then after a few seconds, enable Connection Type. Make sure Authentication Code is left blank. Try to click Reconnect button as well.
In RMS, select the device. Go to Device → Manage services. Check if service, monitoring, auto-extend (optional) are enabled.