GST return defaulter notice requires filing within 15 days or assessment under section 62, with interest and penalty. Notice under section 46 requires a registered taxpayer to furnish the prescribed GST return within fifteen days; failure will prompt assessment under section 62 based on available material and attract interest and penalty, with the notice withdrawn if the return is filed before assessment. A variant requires submission of the final return after cancellation under section 45 within fifteen days, failing which liability will be determined from available or gathered material and interest will be payable; filing before assessment withdraws the notice.