Where in GSTR-1 to show B2C Sale through E-Commerce Operator?

Assesse has sold few goods as B2C (Intra as well as Inter State) through Flipkart and he files GSTR-1 quarterly.

Now, as per my knowledge, these sales need to be reported in GSTR-1 under B2CS(7) column by selecting the type "E". But, while I am filing the GSTR-1 through offline utility, in excel format, I selected "E" then statewise reported the Taxable Value. But, at the time of processing the data, error was showing for these sales. I tried to insert these sales directly in online mode, but no where I found the option where the E-Commerce sales can be reported.

Please help regarding the matter.

Thank you.