GST treatment of transfer of development rights and long term lease premiums clarifies exemption and reverse charge liability on un booked residential units. Services by way of transfer of development rights (TDR) or Floor Space Index (FSI), and upfront amounts for long term land leases used for construction of residential apartments, receive an exemption calculated pro rata by carpet area; promoters must pay tax on the proportion attributable to residential apartments that remain un booked at completion or first occupation on reverse charge, subject to caps for affordable and other apartments, with deemed valuation rules tying values to similar apartments and added definitions including apartment, promoter, project, carpet area and FSI.