Is it possible to add a field (Order Number) to an invoice in Quickbooks Online?

1. I'd be pleased to help you with adding a new field in QuickBooks Online, tmccar.

QuickBooks Online offers a user-friendly method for adding a new field. You can use the Custom Field feature to create a field for the Old Number.

Please be reminded that this feature is only available in QuickBooks Online Essentials, Plus, and Advanced.

Here's how:

1. Click the Gear icon at the upper-right corner and choose Custom field.
   
2. On the custom field screen, click on Add field.
   
3. Enter the necessary information and hit Save.
   

Once done, you can see this field in your templates. See the sample screenshot below.

You can get more details about this feature in the following article: How to add custom fields to sales forms and purchase orders.

Additionally, to help guide you with utilizing your sales form templates in QuickBooks Online as well as on what other information you can add, you can go through the pointers below:

Customise invoices, estimates, and sales receipts in QuickBooks Online.

Add, customise, or remove logos on sales forms.

I'll stick around if you need additional help with QuickBooks. I'm always here to keep helping.