W3 Trends offers an app that might work for you:
You can reward representatives with redeemable points for doing tasks.The Campus Reps app allows you to easily create rewards and tasks for your "campus reps" to complete. Assign points to the challenges, which the reps can later cash in on. They may be able to extend the trial if you need more than 7-days.
We are building an app for the same purpose, It is in beta and should be available in shopify app store sometimes around end of this month. You can however install the app from our website goaffpro.com and see if that fulfills your requirements. As a promo, we are upgrading everyone to enterprise plan forever if they participate in the beta program.
Hi Daria! We recently launched a free referral program app Talkable Referrals https://apps.shopify.com/talkable-lite. It is easy to integrate and free; you can customize design and campaign rules: what reward you will give to brand advocate and their friend. Let me know if you need help with setting everything up.
I just launched our app Gravy Referrals on the App Store, and would be happy to give you a lifetime free account to help with honing new feature requests etc. It operates as an affiliate program as well as a customer referrals app. You can pay for referrals via Paypal or store credit currently. I could look at adding free products as an option too. Let me know what you think.