WBGST DIN introduced for GST communications; recipients can verify authenticity online and post facto DINs issued in exceptions. The Directorate mandates electronic generation and prominent quoting of a WBGST DIN on specified GST communications issued by officers not below State Tax Officer from designated offices, except where GSTN portal numbers are used, communications originate from non-designated offices, or certain forms are manually issued outside office. The DIN's structure, verification via the Directorate website, and initial categories requiring DIN (summons, arrest memos, search authorisations, inspection notices and related notices/intimations) are prescribed. Technical or urgent field exceptions allow post facto DIN generation within three working days; absent DIN, communications are deemed invalid.