PayPal transaction costs

There are no fees associated with using PayPal to donate or pay for purchases or other type of commercial transaction, unless a currency conversion takes place during the transaction.

Could it be a cash discount?

https://imgur.com/a/WIBOgWK It seems that a transaction fee has been charged? There was indeed a currency conversion from USD to euro, but it seems to me that this would not be charged in this way?That's exactly 5%. You could print this out and add it as proof of costs if you can't find any other proof. That's what I would do. It's best to take this into account in future and add 5% to the invoice.

Is that valid proof? Or could I get into trouble with that?
Thanks in advance for your help!

If you don't have any proof, this can count. It's like a petrol receipt that you forgot to print at the station. In that case, the statement is sufficient.

Thank you for your help!