The ‘buy one get one' free movie ticket offer by VISA involves multiple parties. The agreement between the parties must be studied to assess the VAT impact. As a guideline, you can refer one article by Mr. Deepak Agarwal, https://www.gccfintax.com/articles/vat-implications-of-a-multiple-entity-loyalty-programme-955.asp The article can be useful in understanding the details of the scheme and concluding the VAT impact.

Buy one and get one free movie ticket offer involve three parties or more. If we assume that there are 3 parties involved, the seller is charging from the customer with discounted price and charge Vat on the same. And for free ticket, seller is charging the amount from third party with Vat.