Buy X Get Y discounts now support setting a fixed amount discount. This new option can be utilized alongside the existing percentage or free item discount options for a minimum qualifying purchase.
Use this option to create promotions such as “Buy 2 items, get $20 off”. This option is available as both an automatic discount or a discount code using the Discounts GraphQL API.
For more details on how to implement this new feature, refer to our API Guide in the Shopify Developer Documentation.