If your rCell 300 has steady green LEDs for Internet and Power on the side (not flashing), it likely checked into Device Manager. Note: This might take up to 5 minutes. If you are not using a GNSS antenna, the location LED will not be a steady green.
Once your rCell 300 can access the Internet, it will automatically check in. Create your account on https://cloud.multitech.com to see if it checked in. Note: Use your work email as future shipments will get added to this account automatically.