Hello!
I want to ask you if it can happen.
When they buy a product from my site, I give them a second specific product for free.
Thanks!
@Krasimir1 to add product to cart automatically use need to use a App https://apps.shopify.com/gifter-cart-auto-include
Or you can create a Auto discount coupon code. If user adds the coupon code then they will get the free product.
Hope this helps
Thands