GST on Joint Development Agreement(JDA)

Please clarify me regarding GST Payment in JDA. As per Notification 4 of 2018 Land owner has to pay GST (18%) on supply of development rights to the Developer in exchange for transfer of ownership rights. The same notification says that developer is liable for payment of GST on the supply of development rights to land owner. Please clarify Who has to pay GST . Whether both have to pay? At What time they have to pay? In other words I understand that land owner has to pay GST when JDA is signed and development rights are given or passed on to developer. Developer has to pay GST when the apartments are handed over to land owner after completion in all respects.Some people are of the view that Developer has to pay GST at the time of JDV only as the number of apartments are demarcated in that.If both have to pay GST it will be much more(36%). I request you to kindly give me clarification on this aspect as the notification is not clear it covers both owner and developer in clause (a) and (b) Thanking you