Paypal — Currency conversion fees structure

Address:

Hinjewadi, Pune

Hi team,

Please provide us currency conversion fee structure.
On 15 March $21 is deducted as a transaction fee, however we did work of full $400 but we received only $378, which is huge amount for us.
Please provide us the currency conversion fee structure so that we can include same cost in Client's Invoice and share invoice to client including this fee.
Our clients are in US.
transaction done in USD. please share transaction/currency conversion fees per dollar or per transaction.