Do we pay promotion fee?

Hello @Seller_aqStkjSKpfk5Z

Depending on the product category, a minimum referral fee can apply to all products in the buyer's order.

If a buyer purchases product "A" and gets product "B" for free, we charge a referral fee on the total sales price of product "A." Depending on the product category, both products "A" and "B" might be subjected to a minimum referral fee.

You can verify the below help page link (Referral fees for orders with promotions):

https://sellercentral.amazon.com/help/hub/reference/G202134700

Veronica_Amazon