@Mloraditch, @Skachroo, yep, my mistake, you can't get an Advanced Security license for a VMX. They don't have that option, because they don't support that capability. Its worth noting though, that this is one of the few exceptions where you can use an ENT license when the rest of the organization is licensed for Advanced Security.
If this is for Azure its worth checking with your Meraki rep whether its supported or not as Azure still isn't listed on the Meraki website yet, https://meraki.cisco.com/product/security-sd-wan/virtual-appliances/vmx-large/. Supposedly its meant to be happening soon...