Opponent A has Frey Hospitality as their plot card
Opponent A attacks Opponent B with an Intrigue challenge.
Opponent C supports B and steps in with support but loses the challenge.
I know Opponent B must pay the claim ( intrigue challenge ) but which opponent pays the Frey claim effect, is it C ?
C loses the challenge, not B. Look at it this way, if C had won
the challenge, it would be C who could trigger "after you win a challenge" effects, not B, right?
Since C lost the challenge and Frey Hospitality hits "that player" who loses the INT challenge, it's C who is on the hook for the plot's passive effect.