What happens when the discrepancy is not rectified either by the supplier or by the ecommerce operator?

Where the discrepancy is not rectified by the e-commerce operator, an amount to the extent of the discrepancy will be added to the output tax liability of the supplier in his return in FORM GSTR-3 for the month succeeding the month in which the details of discrepancy is communicated.

(ICAI FAQ PUBLICATIONS 06-09-2017 RETURNS : FAQ NO.49)