I can add other expenses on invoices, even when I didn't put on the estimate, or this will not discount to the total of estimate?

You can convert an approved Estimate into an Invoice, then edit the invoice and apply any applicable discount that you choose, if you have the discount feature turned on in account settings.

Welcome, @denisse-realyvaz.

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.

For your reference, you may visit this article for more information: Enter billable expenses.

That's it! But if you're referring to something else, you can leave a comment below by clicking the Reply (green) button. Take care and enjoy the rest of the day!