Special audit under section 66 requires the registered person to obtain a Commissioner nominated accountant's audit of books. Directive orders a special audit under section 66 during ongoing scrutiny/enquiry/investigation, directing the registered person to have books of account and records examined by a chartered accountant or cost accountant nominated by the Commissioner. Issued via Form GST ADT-03, the communication identifies the recipient by GSTIN, name and address, references the tax period, and requires compliance with the nominated auditor's examination, with issuer's signature and designation recorded.