Refer & Earn

I need to implement Refer & Earn functionality in my existing website.
Where user can login and register and get code to share with friends and will getting x% in commission in their wallet. As admin, we should be able to track which all users referred x,y,z person’s and that was total sales and their commission etc.

(Apporx. 50% of work is already completed in it by my current developer but due to health issue he is not able to work on it but he has most of the frame work done and APIs will be given to you)

Site Specification:
Node js based APIs, core Vue js based admin, nuxt js based front website, database is mongodb.