I can share some information in customizing invoices, @catherine-casace.
At this time, you can only add the client information (name, email address, and address) on the invoice. The feature to add PO numbers, supplier account information is currently unavailable. Yes, you can add them in the Message box in the meantime.
I can totally see the importance of being able to add custom fields in creating invoices, so I'll take note of it for consideration in future updates.
I'd encourage you to visit our Blog to be updated with our latest news and updates. We will also be posting our road-maps here, including suggestions received that have been taken into consideration.
You can refer to the following article for more information about creating invoices in QuickBooks Self-Employed.
I'm always here to provide help and answer any questions that you may have with invoices and or anything else. Have a great rest of the day!
We're unable to provide the exact turnaround time as to when a feature will be available in QuickBooks Self-Employed. With this, let's consider letting our product developers know about your request by sending feedback. I'll show you how.
On top of that, I've also included this reference helpful with the resources needed while working with us: Browse all articles for your QuickBooks product.
Don't hesitate to post again here if you have other questions or concerns with QuickBooks tasks and navigations. I'm always around happy to help. Take care and stay safe!