That video explains a lot. It definitely looks like a bug in Paxful's software, but it could also be malware on your computer.

If it is a Paxful bug then perhaps it occurs when you try to send the full balance and there is not enough left over to pay the "network fee", and that confuses Paxful.

If it is malware, the malware is possibly intercepting your input and somehow inserting a request that sends the money to the scammer first, then Paxful gets your request and there is no money left, so it shows an error.

The wonky numbers in the error message ("Please add $-84.35 ...") lead me to believe that it is more likely to be a Paxful problem.