Suspension of registration under CGST rules triggers notice, thirty-day reply requirement; proper officer may revoke or cancel. Suspension of registration under sub-rule (2A) of rule 21A is to be effected where return comparisons show significant anomalies threatening revenue; intimation is sent in FORM GST REG-31 or published as FORM GST REG-17 on the portal. The taxpayer must reply within thirty days in FORM GST REG-18 explaining discrepancies or completing compliance. After reply or expiry, the proper officer reviews and may drop proceedings by FORM GST REG-20 or cancel registration by FORM GST REG-19, changing the GSTIN status to Active or Cancelled Suo-moto.