If I allow a customer to pay their invoice with a credit card do I have to pay a percentage? If so, how much?

Glad to see you in the Community, Adria. Allow me to share how the standard payment fees work in QuickBooks Online.

Yes, QuickBooks will be able to charge you a percentage fee if your customer pays their invoice transaction via credit card. Please note that fees are always subject to changes. To stay current with the latest updates, visit this website to see the present rate for customer charges per transaction: Standard Payment Fees and Rates.

In addition, you can check this article to learn how to set up pay-enabled invoices in QBO: Take and process payments in QuickBooks Online with QuickBooks Payments.

I'm still here to guide you if you need further assistance with payment methods or any QuickBooks-related questions. I'll be around to answer them for you. Take care.

@adriacopeland-gm 

If you run a B2B company, you can use a 3rd party solution to accept CC payments for free.