GST vide Notification No. 08/2020 dated 2nd March 2020 determines the value of supply of a lottery shall be deemed to be 100/128 of the face value of the ticket or of the price as notified in the Official Gazette by the Organising State, whichever is higher.
http://cbic.gov.in/resources//htdocs-cbec/gst/notfctn-08-central-tax-english-2020.pdf