I can help get rid of the error so you can generate the GSTR1 report, shreyans@moxiesu.
The error you're getting can be caused by an old cache piled up on your browser. To fix this, let's log in to your QuickBooks Online account using a private browser window.
Try these keyboard shortcuts depending on the browser you're using:
Google Chrome: press Ctrl + Shift + N
Mozilla Firefox: press Ctrl + Shift + P
Safari: press Command + Shift + N.
Once logged in, go run back the GSTR1 report. In case you need a reference, let me share the steps on how to pull the report below:
Go to the Reports on the left menu.
Under GST returns, choose GSTR1- Summary of outward supplies report.
Customise the necessary filters like the Report period and Accounting method.