Late fee waiver for delayed GSTR 1 filings where outstanding returns were furnished within the notified compliance window. A proviso waives the amount of late fee payable under the Act for registered persons who failed to furnish outward supply details in FORM GSTR 1 for specified past tax periods but who furnished those details within the notified compliance window; the amendment is effective retrospectively to the start of that window and applies solely to late fees for those delayed GSTR 1 submissions.