The gift thing is not useful to the case.
I see you 2 agreed on $1600 split over 2 days. I see he acknoledged receipt of $800. Do you have a screenshot of sending the second $800? And do any of your screenies have the dates in them by chance? May want to take a small snippet of paypal transaction, just to show date, receivers email and amounts.
Do you have screenshots of the other party asking for more than $1600?