Through the Finance Act 2015 ,Section 56 has been amended and clause ix has come into effect from 01/04/2015 . As per this - Any sum of money received as an advance or otherwise in the course of negotiation for transfer of capital assets if (a) such sum is forfeited and (b) the negotiation do not result on transfer of such capital assets .
Here in this case , the amount that you have paid has been forfeited and the capital assets ( flat ) has not been transferred . Hence taxable under the head " Income from other sources " .