15 June 2021
Section 15 deals with valuation of vouchers. Refer that. Apart from that you should take professional opinion as there are many factors involved in it. The business model also plays an important role in determining supply.
17 June 2021
I agree with CA Altamush because this is not a simple question, It will require more details & will have to be dealt with various provision of GST ,
Its Better you meet a professional in personal and have a discussion.