Hello rachel25,
This is a great question. I'm glad to see you've discovered how to add custom fields to your invoices. I'm happy to go over how they work.
The custom fields you can add to sales forms can be just about anything you need. Because of that, the program doesn't auto-populate the fields because they aren't linked to a specific area of the program to pull the information from. Filling in the field with what you need each time you fill out the form will ensure the information is included.
Feel free to leave feedback about this feature by going to the Gear icon in the upper right of your account and clicking Feedback. These comments are shared with the product development team for consideration in future updates.
Learn more about customizing sales forms here: Customize your invoices, estimates, and sales receipts in QuickBooks Online
I'm here if you have more questions. Enjoy your week!
