Hi there, @HBDesigns. I'll share some information about how you can add the credit card processing fee to your invoices in QuickBooks Online (QBO).

To add a credit card processing fee to your invoice, you can create a service item, then manually add it to your invoice. You can also consider a third-party app and integrate it with your QuickBooks. To begin, these are the steps:

1. On the left navigational bar, go to Get paid and & pay tab.
2. Choose Product & Service.
3. Click on New then select Service.
4. Enter the name of your service item. (Example CC Fee)
5. Select the account you'd use to track the processing fees.
6. Once done, click Save and Close.

Once done, add the credit card fee as an additional item on your invoice when you charge your customers with the processing fee.

In case you'd like to use a third-party app, here's where you can find one in QuickBooks Online:

1. Sign in to your QuickBooks Online Company.
2. Go to Apps tab.
3. On the search bar, type the name of the that you'd like to integrate with your QBO account.
4. Click the Search icon.

For visual reference, you can refer on the screenshot below.

Feel free to visit these handy articles for future reference:

• Customize invoices, estimates, and sales receipts in QuickBooks Online.
• Record invoice payments in QuickBooks Online.

Know that I'm just a click a way if you need further assistance with this. Have a nice day!