Can I limit Advocate/Friend discounts to a [specific collection / free product / free shipping]?
Conjured Referrals now supports limiting discounts by collection or product! Simply change the "Applies To" select box to "Specific Product" or "Specific Collection" and pick your collection/product, and you're good to go!
Currently, our app does not have a way to automatically limit discounts to free shipping, however you can accomplish this by selecting the "Manually-Added Custom Codes" reward type, then manually adding bulk-created discounts on the Rewards tab of the Campaign Details page. You'll need to keep an eye on how many codes you have left to ensure you don't run out, and periodically add new ones since the app won't make the codes for you automatically in this case.