A transaction fee is considered an expenditure, and I understand why the business you're helping wants to pass it to its members. I'd like to share information about it.
Please know that this practice is not legal in some states, and Intuit may be subject to a card brand fine if we allow this. We also explained in bullet #12 in the Prohibited Processing Practices section of the INTUIT TERMS OF SERVICE that we do not encourage the passing on of credit card charges (surcharge) to customers unless allowed in your state.
And I quote:
"You may not add any tax or surcharge to transactions, unless applicable law expressly allows or requires you to impose such tax or surcharge. If any tax or surcharge amount is allowed or required, such amount must be included in the transaction amount and shall not be collected separately."
If your state allows surcharging customers for a credit card fee, you can add it as another line item on your invoice, like in the screenshot below. Then, feel free to submit a feature request so this will be considered in future updates.
On the other hand, if you like reading articles about QBO and QB Payments, feel free to check them out on the main support page, and choose the said products.
Please don't hesitate to comment below if you have more questions about the processing fee or anything about QuickBooks. The QuickBooks Team is always available to help.