You're gonna need a wireless point-to-point bridge. Repeaters are shit, and won't work over that distance and into a pole barn with metal walls. Neither will an outdoor AP on the house side. I don’t think the U6 Lite supports PTP mode, either.
Basically, two of these, with Ethernet ran from the router through the wall facing the barn on the house side and into one, then the other on the pole barn exterior wall facing the house, and Ethernet ran through the wall there to an AP or a router in bridge mode broadcasting WiFi for the barn.
Note: There has to be direct line of sight between the two for it to work.
https://www.amazon.com/Ubiquiti-NanoBeam-High-Performance-airMAX-NBE-5AC-Gen2-US/dp/B0713XMHH9