All my data is lost (customer invoices) and the sync data button is grayed out

I can help you perform troubleshooting steps to resolve invoice data issues and sync option in your account, Mithra.

When running QuickBooks Online (QBO) within your regular browser, sometimes stored cache files can cause an interruption while using our features. To help you fix this, you may consider opening your account in a private browser to ensure the program runs without storing cache files. You may use these keyboard shortcuts:

• Google Chrome: Ctrl + Shift + N.
• Mozilla Firefox and Microsoft Edge: Ctrl + Shift + P.
• Safari: Command + Shift + N.

If you're able to successfully modify and run the report without having issues, you can go back to the regular browser and clear its cache or use a different supported browser to remove the temporary files.

Furthermore, you may refer to this article to guide you in reviewing and tracking customer-paid invoices in your file: Record invoice payments in QuickBooks Online.

I'll make sure to get the help you need for any additional queries when managing and running financial reports. Just leave a reply in the comments below. Stay safe.