Hi @EnggCollege , has the 450 ever registered out to the cloud? The MX can’t register using cellular fresh out the box.
Secondly, is your dongle in the supported list:
https://documentation.meraki.com/MX/Cellular/3G%2F%2F4G_Cellular_Failover_with_USB_Modems#Supported_...
Darren OConnor | doconnor@resalire.co.uk
https://www.linkedin.com/in/darrenoconnor/
I'm not an employee of Cisco/Meraki. My posts are based on Meraki best practice and what has worked for me in the field.