@Netwow if you are using any form of Wireless WAN router/modem that has an Ethernet hand-off then you will need to connect it to a WAN port on the MX, which will mean you will have some charges on it. These charges come from the fact that every WAN port on a MX will constantly connect to the Meraki cloud to ensure it has connectivity - this will be in the region of about 100MB a month (from what I've seen) - and you can't disable it.   You can stop the MX from forming AutoVPN tunnels on all interfaces by going to Security & SD-WAN -> SD-WAN & Traffic Shaping and disabling the 'Active-Active AutoVPN' option. This will mean that the AutoVPN tunnel will only be formed on the primary link unless it fails, so keeping the traffic to a minimum.   The only way to have a true failover function (where there is an absolute minimum of traffic on the 4G circuit) is to have a USB connected modem, or to use a MX model with the in-built 4G/LTE modem. ... View more