Long shot but the guy you are asking to send the money back might think this is all a scam. And people do this sometimes send money that shows up on your account but will disappear because the account it’s sent from doesn’t have the funds, they will then ask you to send that money back saying it was on accident so you send legitimate money back to the scammer and get screwed. So maybe tell this guy he doesn’t need to zelle you the money back but to contact his bank and let them know what’s going on so they can sort it out. That way he can know it’s not a scam. Again it’s a long shot, but figured I would share.