Welcome to the Community. I'd be happy to provide some information about adding a transaction processing fee on your invoice.
Are using the Merchant Services when processing payments for invoices? If so, being able to add the credit card processing fee for your customer's invoice isn't applicable. This is because the credit card processing fees are required every time you do a transaction.
For example, your invoice amount is $3000, and you're going to add a 3% fee which is $90, so the total invoice amount would be $3090 (invoice amount and the credit card processing fee). By the time that your customer is going to pay the invoice, you'll be paying a 3% credit card processing fee since the charge will happen every time you process a payment.
For you to receive a payment for the credit card processing fee, I'd recommend having an internal agreement with your customer.
To learn more how credit card processing fee works in QuickBooks, please check out these articles:
My merchant service always charge a fee for paying with debit or credit card.
my Question is basically if Quicbooks offer an option for customer to pay the fee instead of me, I think QB can ask if agree to add the fee to any invoice automatically making a payment with credit card.
Out of all 100 invoices I have sent , only 2 paid with credit card, the rest give me a check, but i notice QuickBooks offers bank transfer free of charge and credit card reading or entering manually option with 2.4%+$0.25 per transaction.