VLAN tag single LAN port on DDWRT router

**My issue:** I want to VLAN tag a single LAN port for a IoT device, wired to a DDWRT router, which is acting as a switch/AP... Under networking in DDWRT, if I select the port, and tag VLAN 2 the device on the port goes offline. What config do I need to set on the DDWRT, in order for a single port to allow provisioning of an IP on my VLAN 2 tagged network with DHCP from the upstream router (UDM Pro)? **Background:** I have a DDWRT router in my office acting as a managed switch/AP. I have a UDM Pro upstream as the router. I want to allocate a single LAN port on the DDWRT, to VLAN tagged 2. Anything connecting to the port should get an IP from my tagged network, as configured (DHCP) on the UDM Pro. Other ports, and WiFi AP stuff should be normal untagged LAN. I have a network on my UDM Pro for the tagged VLAN, including DHCP server. *Importantly*, with the downlink port profile on the UDM Pro set to VLAN 2 *only*, and *without* the DDWRT in the middle, the wired device correctly gets an IP from the VLAN DHCP. So my UDM Pro is working as expected. I now want to put the switch (DDWRT) in the middle. All ports, normal LAN, but one port for this device to get an IP on the tagged VLAN. The UDM Pro uplink is now delivering "All" (which I will narrow down later). I understood this to mean it would transit both tagged and untagged traffic, which is what I want since both will coexist on the DDWRT.