Revocation of cancellation of registration: procedural application and officer discretion govern reinstatement process. A cancelled registrant may apply for revocation using FORM GST REG-21 within the prescribed period, except where cancellation resulted from failure to furnish returns unless those returns are filed and all tax, interest, penalty and late fees are paid; the proper officer may revoke by FORM GST REG-22 if satisfied with recorded reasons or, after issuing a show cause in FORM GST REG-23 and receiving a reply in FORM GST REG-24, reject by FORM GST REG-05, disposing of the application following prescribed procedural timelines.