Let's get this working, userabclothingss.
Mobile applications normally collect cache files that help to save you time while browsing. Sometimes, these files can become outdated or corrupted, causing issues like you're experiencing with the invoice numbers. Clearing the app's data can fix it. This can be done on the app or on your phone settings.
You can refer to this article for entire details of the troubleshooting. You may notice that the article may be for United States but is applicable to global versions like India: Mobile App's troubleshooting.
You might want to check out this article in case you want to customise your invoices: Customise invoices on the QuickBooks Online mobile app.
If you're using QuickBooks Apps, I've added this article for troubleshooting steps: QuickBooks App for Windows General Support.
Also, feel free to visit these links where you can gain more tips and articles for future use:
Let me know if there's anything I can help with by leaving a reply below. I'd be glad to help. Have a good one.