Dear Sir,
Hope you are doing well !!
Yes, it is vaild.
You need to take proof from builder that he paid the GST to the government which you had paid to builder.
Once you cancel the booking, the builder is liable to refund your booking amount after deducting agreed penalty charges
However since the builder would have already deposited the GST amount with the government, the builder is not liable to obtain refund of that GST
For the refund you will have to make an application to the GST Council seeking refund as your booking is cancelled.
We have handled such cases before.
We may assist you in entire procedure.
It is advisable to take a phone consultation for detailed discussion.