Gstr 1

you have to follow these instruction

1- month of july you have to file individual not mixup with aug and sep data

2- using offline tool select september month and give aug and sep data ( not july) then generate json

3 - go to portal first file your gstr 1 july individual
then select septmber and upload your json

then you face no error there

I did exactly the same. I filed GSTR 1 for July in August itself and for the month of Aug and Sept., i did exactly what you just said. Still, the issue persists and is not resolved.