It is risky to look these receipts from developer by individual residential flat owner - in isolation - to determine gst liability.
One needs to look into entire arrangement of redevelopment of society (as there are many different ways such arrangement can be worked out) by holistic reading of agreement/s entered into, between builder, concerned society and its member-constituents before addressing issues raised in the subject query.
For just example/s among many possibilities: Subject receipts can be in nature of 'liquidated damages' not liable to gst. They also can be part of 'consideration' paid by the builder towards overall arrangement agreed between all concerned parties and thereby, liable to pay GST.
The plea that 'these receipts are not in the nature of furtherance of business hence no supply' cannot be looked into in-isolation, specially considering very broad definition of 'business' u/s 2 (17) of the CGST Act, 2017.
These are ex facie views of mine and the same should not be construed as professional advice / suggestion.