What is the solution to Protagoras' Wager?

Perhaps there is no solution but I thought I’d give it a go:

Protagoras teaches law (well, “sophistry” but you get the point). Eulathus is one of his students but has no money to pay tuition. The two make an arrangement: Eulathus will pay the tuition after he wins his first case. Indeed Protagoras guarantees that Eulathus will win his first case. Upon completing his training however, Eulathus doesn’t argue any cases and never pays. Annoyed, Protagoras sues his former pupil.

“Either I win and you must pay me, or you win, and thus having won your first case, you must pay me.”

“No,” says Eulathus. “If I win I am not required to pay, and if I lose, I have lost my first case, and am not required to pay you.”

Is there a logical error in this paradox? Who is right? Can they both be right, or are they both wrong?