1) X does not have the funds to pay for allotment letter
2) Y is willing to provide 20 per cent advance for purchase of property and on receipt of allotment letter pay the balance amount
3) it is win -win situation for both parties
4) your agreement with Y should contain clause that balance 80 per cent would be paid within 3 months of receipt of allotment letter
5) in the event Y fails to pay balance amount within 3 months 20 per cent advance would be forfeited