IGMP Snooping on LAN

The only reference I can find in Peplink documentation to enabling IGMP snooping is while adding a new SSID - how can I enable for LAN?
Application is livestream video transfer between mobile user and fixed site with routers linked via PepVPN; link is up and ping from encoder-side network to decoder-side router and decoder device OK, as is web gui access to both encoder & decoder from same PC but the devices do not establish the stream link. Devices work fine on same office LAN (wired ethernet only in the devices), but when both connected to the same Peplink router there is no video link. I note in the encoder docs: “IGMP snooping must be enabled on your network device”

Update: actually the devices connected to the same router did work (create the visoe link) after resetting IP config in the device (schoolboy error) but still not over the VPN