Refer a Friend v1.1 is working just fine with WooCommerce 3.0 as long as you are not using “Product % discount” coupon type, because from 3.0 this product type is removed from WooCommerce and can not be used anymore. So you need to use one of the three other coupon types (Cart Discount, Cart % Discount or Product Discount), as per image:
We pushed “Refer a Friend PREMIUM 1.1.1” update, which removes “Product % discount” from this dropdown and also fixes some notices which can show up if you have debugging mode enabled.
Update will show up under your site plugins page, if you have connected licence key with your site and did previous update that enables this. You can read more on how to update plugin at the bottom of our previous post.