I want to deliver property but client is not accepting

Avoid committing anything in writing, except as a reply to such notices denying those statements in notice.  Explore the possibility of raising some finance or dispose of the flat or contact an advocate for further guidance in case your receive a notice.  Because it is a friendly transaction retain friendship understanding the other side's concern.   He can not demand any other thing, yes he can demand refund of such amount, with interest or compensation for harassment only after proceeding through a court of law.  I do not find any criminal intention as it is he who has cancelled and demanding the amount and there is civil dispute.

Hello,

Your friend's demand of Rs. 50 lakhs is unreasonable. But you suppose to hand over possession as per agreement or within a reasonable time. You have agreed to return the amount but out of 12.5 lakhs, you return only 5 lakhs that too in April 2019. In your case, you are liable to pay compensation and interest etc. If don't pay police will register the FIR and arrest you. 

@SHRISH PAWAR

I am ready to give remaining amount in 2019 but from August 2019 he started demanding 50 lakhs or flats in Kharghar. And started severe harrasement and continue till now.  Also forced us to sign one fake notary of kharghar property in September 2019 which I don't know which mentioned the amount of Rs.25 lakhs and continuously warning that we will murder you. Now with Fake agreement they registered a complaint in crime branch. Suggest me what to do now? 

The facts posted suggest a civil dispute; police have no jurisdiction to interfere or register FIR. All that your friend is entitled is the return of his money with reasonable interest. Other demands alledly being made by him are too extravagant to be legally enforceable.

Such commercial query should be advised by engaging a prudent lawyer, which you can afford.