I have a question about the cart price rule-coupon for "buy one get one". The functionality I want is for a customer to buy a certain amount of a product, enter the coupon code, and then get a free separate product. Every time I've tried this it didn't work. I was able to discount the product that was originally entered, but I couldn't add an "add-on" product if you will. Is there a way to get this functionality using the "buy one get one" coupon?
There are 2 options for you here. The first one is more complicated and less automated, while the second one will work flawless but it requires a plugin.
1) You can find detailed info here:
2) You can install this extension, and it will do the rest https://amasty.com/free-gift-for-magento-2.html
Hope that helps!