HUAWEI E8372 USB stick works great with MX64 and most APs, even Z3. I mostly use it a cellular backup. Private APN configuration is made on the modem itself and connectivity should be tested on a PC before deploying on the MX. ... View more

@PhilipDAth has a great point, use one of the WAN ports if you can.  If not I would get a new modem for your 3G/4G line of service and utilize the USB port.     See here: https://documentation.meraki.com/MX-Z/Cellular/3G_-_4G_Cellular_Failover   Ryan      ... View more