I've got you covered today, Kelly. 

Adding a commission rate in QuickBooks Online can be done if we create a service item. Once done, we can add this item to your invoice on how we get the commission. 

Here's how to create a service item for the commission:

1. Select the Gear icon and then choose Products and Services.
2. In the Products and Services window, select New.
3. Select Service.
4. Enter the service information (you may type in commission on the Name field) and click Save and close.

Here's how it'll look like when you create an invoice.

After that, you can open or edit the invoices and commission from there to match the receipt manually. 

We can browse these articles for more details:

• Add product and service items to QuickBooks Online.
• Create invoices in QuickBooks Online.

Let me know if we have any other questions about adding commission item. I'm more than happy to provide additional assistance. Wishing you a good one!