Cannot Submit GSTR1 for this Return Period

June 2020 is not over yet, The error may come because of that. Please try to file June 2020 return after June month. The issue may get resolved

You cannot file GST return before completion of a tax period. 

For June the tax period ends on 30.06.2020. Only after this date you shall be allowed by the portal to file your GST return. 

You cannot file returns in advance for a tax period for obvious reasons.

I hope this helps!

For any further assistance on the above, you can contact me at connect @ ujlegal.com 

 GST return cannot be filed  before completion of that tax period for which return is being filed.