Ask HN: Referral program as a service?

Hello,

We are an e-commerce company looking into building a referral program where users who refers a friend will earn some credits as discounts and also give some credits to the referred friend. Something along the lines of Uber and AirBnb referral program.

Does anyone know of any companies that provide such services with an API?

At first it seems a simple thing to build, but an entire business could be built around it as we can have many rules regarding such promotions and as a bonus point it could also handles coupons (validation, expiration, level of discount, etc)

Thanks!