Same error here also. We had raised the ticket but poor resolution from GST technical team. They closed the ticket twice without consent from user. We have now raised the grevience for the same.
Dear All, Please Kindly Download Opera Browser. Also change JSON File extension from JSON to JSO by renaming it. Then try to upload it through opera browser. It will works. Just now I did the same and it worked.
Statement 3 Excel Utility provided by the GST portal (for RFD-01A) is not working. The file says it is read only. Please help if someone found a way out.