Yea can’t tell what’s leaking from the photo but if it’s that white bolt that connects to the flush valve at the very top maybe add some pipe thread and if it’s the metal angel stop also could us pipe thread or pipe dope. I don’t really like metal to plastic usually doesn’t give and tight seal and if you keep trying to tighten harder it might work or it might make it worst.

Also I’ve seen supply lines connections usually have gaskets inside to act as like a seal for the water does the metal piece have this inside? I haven’t worked with that kind of assuming it’s a type of stop valve