What does Paul tell Philemon to do with anything Onesimus owes him?

Answer: Charge it to Paul's account

Paul writes, "If he has wronged you in any way or owes you anything, charge it to my account... I will repay it."

“But if he has wronged you in any way or owes you anything, charge it to my account. I, Paul, write this with my own hand. I will repay it—not to mention that you owe me your very self.”— Philemon 1:18-19 (BSB)