Input Service Distributor rules for pro rata allocation and recovery of wrongly distributed input tax credit. Input Service Distributor (ISD) is an office that issues a prescribed document to distribute input tax credit of CGST, SGST/UTGST or IGST to suppliers with the same PAN. ISDs require separate registration; distribution is limited to recipients who used the input services and to operational units to which services are attributable. Where direct linkage is not possible, credit is distributed on a pro rata basis based on recipients' turnover in the State/UT, not exceeding available credit. ISDs file monthly GSTR-6; excess credit is recoverable from recipients with interest under recovery provisions.