Non-filing and short-filing of GST returns trigger automated defaulter notices and invalidate returns for matching until full tax payment. Failure to submit periodic GST returns will trigger automated generation of a defaulter list for enforcement, with the GST Common Portal auto-sending notices and displaying non-filer details for officers; system-imposed automatic late fees may apply. E-Returns may be uploaded despite short payment to record self-assessed liability, but such returns will be treated as invalid for invoice matching and fund settlement until full tax payment, and will receive a unique transaction ID and notice.