Universal Plug and Play (UPnP) is a series of protocols for communication between networked devices. It allows for devices to automatically discover, create connections and communicate with each other without additional setup. UPnP is the networking equivalent of Plug and Play which is used for devices like keyboards and other peripherals that are used with client devices today.
UPnP on the Meraki platform is not supported at this time. However, since the standard uses protocols like TCP, UDP, IP, HTTP, and XML, the MX and/or Z1 can pass UPnP traffic within the same broadcast domain (VLAN or subnet). This means UPnP enabled devices will be able to communicate with each other when on the same VLAN/subnet behind the MX/Z1 gateway. If the UPnP devices reside on different VLANs/subnets, they will not be able to communicate because the MX/Z1 does not forward broadcasts between VLANs.
You can learn more about setting up a network and the difference between using a single LAN or VLANs in the MX Series documentation.