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https://addons.prestashop.com/en/promotions-gifts/19646-free-product-gifts.html
Overview
Reward your customers with free add on gifts based on the products they purchase. Easily define single or multiple free gifts for individual products and allow customers to pick their free gift directly from the product page.
What this module does for you
insert_chart Promote impulse buying
Increase conversions by giving away free gift products with selected products. Assign free gift products on a product by product basis and offer your customers the choice to choose their gift from a selection of free products gifts.
What your customers will like
Customer satisfaction as they receive free products when they purchase certain products. For products containing single free gift products product is automatically added to the cart when they purchase nominated products - no fuss, simple and easy for the customer. For products containing multiple free gift products, just one click directly on the product page and their selected free gift is added to the cart when they add the nominated product to the cart.