You can choose how conversions are credited when multiple referral links are involved in a customers purchase, in the “Referral Links” settings tab.

• Last-Click: New referral links overwrite referral cookies and auto-applied coupon with the latest affiliate.
• First-Click: Once a referral cookie exists, later referral links won’t replace it or the cart coupon automatically; customers can still manually apply a different coupon.

Bare in mind: In both cases the referral link cookie will take priority over the cart coupon in terms of awarding the affiliate, if link tracking without coupons is enabled.