Thanks for explaining further what you're trying to accomplish, @KrisG9988.
Allow me to provide some clarification about your credit card processing fee concern.
If you are using the merchant services when processing payments for invoices, 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 charged every time you do a transaction.
Yes, you are correct. When you process an invoice for $5145 (invoice amount and credit card processing fee) you'll still be paying another 2.9% which would be a total of $149.21. That said, you won't be able to receive the full invoice amount.
To learn more how credit card processing fee works in QuickBooks, please check out these articles:
This should get you moving today.
Please let me know if you have more questions about this concern. I'm always here to help. Take care!