Taking the unifi AP controllers out of the equation i.e. assuming they don't attempt to give out dhcp addresses, the in OPN, on Services > DHCPv4 > {VLAN name} > At the top select "Enable DHCP server on the {VLAN name} interface". This is for ipv4 of course, and chose your options.Then you need to have firewall rules to allow dhcp (udp 67 and 68). Creating the VLAN, I think with OPN default options it creates them automagically. Check they're there. If not, you can copy it from the LAN.
Have you tried rebooting after setting up the new VLANs ?Recently had the case where I added a new VLAN.Everything seemed (and turns out was) set up fine, but I couldn't get DHCP to work. Spent a few hours eliminating everything else and finally decided to reboot.Et voila, everything worked as expected after the reboot.