Online invoice payment transaction fees

I have been searching through the help section and can find no information on this issue.

From the customer's point of view when receiving an emailed invoice, if they choose to pay with a card, does QBs automatically add the transaction fee, or is that something we as the vendor need to add into the invoice before sending it?

We have no real experience PAYING QBs invoices by card, so I need to know what happens on the customer's end when they are paying.

Thanks,

Robbin