Hello @Erin Leslie,

You can add a new custom field for your invoice template directly from the Gear icon.

1. Go to the Plus icon.
2. Under Customers, select Invoice.
3. Select the Gear icon at the top-right portion.
4. Click Add another field.
5. Enter the name of your new custom field.

You can also read the following articles below in case you need some ideas about customizing your sales transaction template:

• Customise invoices, estimates, and sales receipts in QuickBooks Online
• Add, customise, or remove logos on sales forms

Fill me in for all of your QuickBooks needs, I'm always happy to help. Thanks for dropping by.