Why wasn't the transaction fee automatically included in my invoice?
If your customer pays by credit card, the transaction fee won't automatically be added to the invoice.
To charge your customer the transaction fee, you must manually add it as a line item when sending the invoice.
If you use eWAY, the fee can be automatically calculated and added as a surcharge when you invoice your customer. To do this, instead of using the eWAY payment service setup screen in Xero, set up eWAY using a custom URL.
eWAY Knowledge Center (eWAY website)