Welcome to the Community space, @Nikki M.

I am here to share some insights on how to show the markup on your invoice when sending it to your customers in QuickBooks Online (QBO).

First, you'll need to create a billable expense, here's how:

1. Click the +New icon. 
2. Choose Expense.
3. Add the Payee's name.
4. Select a category and enter the amount.
5. Check the Billable box and add the customer's name.
6. Enter the needed details.
7. Click Save and close.

Once done, recreate the invoice and add the billable expense.

1. Click the +New icon, then select Invoice.
2. Choose the customer's name from your billable expense.
3. Click the little arrow in the upper-right-hand corner.
4. Select Add on the billable expenses.
5. Click Save.

Moreover, I'm adding this helpful article as your reference in managing your expenses in recording invoice payments in QBO: Record invoice payments in QuickBooks Online.

Please don't hesitate to return to this post if you have other concerns in managing your invoices and expenses in QBO. I'll be here to lend a hand. Have a good one!