I'm using Magento 2 CE Version 2.12
I have followed the below one, as well other tutorials.
Still, it's not working.
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Please create cart price rule and for action tab check below screen shot :
Now please add to cart product with qty 2 and apply this coupon code now you will get one product price as a discount.
Actually there is no any facility that magento give buy 1 get 1 free automatic so we have to add product with qty 2 and apply rule then we get the discount.