Hello there.

The option to edit or change the invoice number in QuickBooks Online is only available in the browser version and not in the QuickBooks Online Mobile app. This difference in functionality is due to the varying features and capabilities of the platforms.
 

To change the invoice number, I recommend using a web browser on your computer or mobile device to access QuickBooks Online. In the browser version, you should be able to edit or change the invoice number for your invoices as a workaround. I've also added this article to learn which QuickBooks Online mobile app features are supported on mobile devices: Compare mobile app features.

You can also use this resource in the future if you need more personalized invoices and other sales forms: Customize invoices, estimates, and sales receipts in QuickBooks Online.

If you have any additional concerns or questions about invoices, please keep this thread in mind. Keep safe!