It's nice to have you here in the Community. I'm here to share some information about adding other expenses to an invoice in QuickBooks Online (QBO).
@Regina_Lend_A_Hand_Accounting is right. Additionally, If you're referring to a billable expense, yes! Once you created a billable expense, you can add this to an invoice without an estimate. Also, this won't discount or deduct the total amount on your estimate unless you include it to the invoice.
To add a billable expense to invoices, here's how:
1. Click the Plus icon at the top, then pick Invoice. 2. Enter the customer name on the Choose a customer field. Any OPEN billable expenses will populate on the right side of the screen. 3. Select Add for the billable expense you want to add in the Invoice. 4. Once done, click Save and close.