To download the error report after a failed GST return, you can try the following steps:
1. Log in to the GST portal.
2. Go to the "Returns" section.
3. Select the relevant return (e.g., GSTR-1, GSTR-3B).
4. Click on the "Prepare Offline" button.
5. Generate the JSON file for the return.
6. Upload the JSON file on the portal.
7. If there are errors, a link to download the error report will be provided.
8. Click on the link to download the error report.
If you are still unable to download the error report, you may need to contact the customer support of the GST portal for further assistance.