Revocation of cancellation of registration: applicants must apply within prescribed period and track the application on the common portal. Application for revocation of cancellation of registration under Form GST REG-21 must be filed on the common portal within thirty days of service of the cancellation order, subject to specified extensions; no fee is payable. Applications are not permitted where cancellation resulted from failure to furnish returns unless those returns are filed and resulting tax, interest, penalty and late fee are paid. The form requires cancellation order particulars, last return details, reasons for revocation, supporting documents and an authorised signatory's verification; certain contact detail changes require online verification.