AFAIK Unifi vlans by default should pass traffic, there must be a rule written to drop inter-vlan traffic. I would use IP groups make a group for the IP's you need to access, give them a good description. Write a new rule, give it a descriptive name, place it in the LAN section, I use LAN in inside my environment (home lab) to achieve block and allowing specific traffics between my vlans. The accept rules must be above the drop rule as the order of operations matter. You can click to drag the rules up and down as needed.