Mistress Domi suffered loses as a result of this old fool and she was so pissed at him that she could not let him walk away after all the losses she had incurred as a result of him. She had to make sure it never happened again and that is why she slapped the shit out of him and also choked him a little. The punishments were enough to make him change his ways.
Mistress Sofi is a control freak and this guy was proving a hard nut to crack. Her manipulation had not managed to ensnare him and she had to come up with a different strategy for what she wanted to do to him. The mistress went ahead and she used her faceslapping fetish to do it. She let the pain get to him and do the talking and the convincing on her behalf.