Warn him of the possible fraud, let him sign some form of agreement but then send the money.
Unfortunately, banks that used to take this approach have been stung by people who listened to the warning, signed the agreement, got defrauded, sued the bank /and won/.
I think most people would be surprised you can win a case if you have been warned.
But if you block my money that's a lot bigger issue.
Revolut customers are forced to take selfies "this is a scam" and they still send the money, and ask it back:
https://x.com/moo9000/status/1790275729634029798
As discussed in length in here (now downvoted):
https://news.ycombinator.com/item?id=41273554
Warn him of the possible fraud, let him sign some form of agreement but then send the money.