Friend's father approved a fraudulent transaction worth $8000 - what can be done?

My friend's father is in his 60s and not that tech savvy. He regularly does large transactions due to his business (fast food joint) and I believe this is why he was targeted. He received a message asking him to confirm if he was doing a 8000 dollar transaction or not. And he believed that this was his supplier and approved it. It turned out to be a fraudulent charge.

It gets more murky here and I have been pulled into this saga quite late. They hired a lawyer who charged them 1500 dollars but could not recover the money because the card issuer said you approved it so they can't do anything about it.

As I understand the maximum liability for a fraudulent transaction is $50. So, what correct information should I give to my friend so that he can recover some money?