The threaded connection looks like it has thread tape or sealant on it ? Brush it clean with a wire brush. No sealant is used on a flare since the angled end is the mechanical joint. The threads are straight, not tapered and only pull it tight. The threads are not used for sealing like on tapered pipe threads that require sealant. Tape on a straight flare or hose thread only binds the threads so you can't feel it tighten properly on the seat.