As a builder Can I offer cash in lieu of flat to landowner ?

I am a small builder and went into a joint venture agreement with a landowner who stayes at USA and US citizenin. The site is in West Bengal. I was supposed to pay him 15 lacs cash and 2 flats ( One flat of 2500 sq ft on 1st floor, another flat of 960 sq ft on 3rd floor) and one shop. GPA and development agreement was made and registered accordingly. I also had to give 4 flats to the relatives of landowner who was looking after the land but this was not known to the landowner. Now the building is ready and his relatives have got their flat registered in their name. In the meantime I had a customer who wanted a big flat on third floor and sold the entire floor to him where landowner allocation was also clubbed. Now I don't have any space in third floor to allocate 960 sq ft flat to landowner as per agreement. But I have a 850 sq ft flat on the 1st floor which I am offering to landowner and differencial amount in cash. I have also offered him an option of payment of full market value of 960 sq ft flat which I was supposed to allocate him on 3rd floor. Need suggestions on this...can the landowner refuse to accept any of the offer and stick to his demand as per agreement? What will happen if I don't have any space on 3rd floor to give him? Request your suggestions on this.