Thank you for posting in the Community, @NealRM.

Currently, the ability to add a convenience fee for paying by credit card is not available in QuickBooks Online.

As a workaround, you would need to create a service item for the credit card convenience fee and manually add it as a line item on your customer's invoice to indicate the fee. Let me show you how.

1. Go to the Gear icon. 
2. Choose Products and Services. 
3. Click the New button. 
4. Select Service. 
5. Enter the name of the of the service item. 
6. Put a check mark on “I sell this product/service to my customers.” 
7. Choose an expense account (for example Other Expenses) from the Income account drop-down. 
8. Click Save and Close.

Here’s how to add the service item on the invoice:

1. On the create invoice page, click Add line.
2. From the Product or Service drop-down column, choose the charge convenience fee you created. 
3. Click Save and Close.

In the meantime, you can visit QBO Blog to learn about the new updates being rolled out by Intuit.

Feel free to post again if you have other concerns. I’m always willing to help.