How do i apply a discount to an invoice using the mobile app?

Let's add the discount field in your invoices, @info-safearborse.

First, you must log in to your account on the web to turn on the discount feature in QuickBooks Online (QBO). Here are the steps: 

1. Go to this link: https://qbo.intuit.com.
2. Click the Gear (⚙) icon at the right top and select Account and Settings.
3. Go to Sales and in the Sales form content section, click the pencil icon to edit it.
4. Mark the Discount box.
5. QuickBooks automatically creates a discount account on your register.
6. Click Save, then Done.

Once done, you can now see the Discount field on your mobile app when creating an invoice. 

Check this article for more information: Add a discount to an invoice or sales receipt in QuickBooks Online.

Also, here's more information on how to Customize invoices, estimates, and sales receipts in QuickBooks Online.

I'm always here if you need help with your invoices. Let me know by leaving a reply below. Stay safe and have a wonderful day!