Creating a Successful Referral Program for Your Newsletter

Hi everyone, my question is about Referral Program. I have a Longevity Newsletter in Portuguese and now I want to create a Referral Program giving people promo codes for products and services. All I found on Beehiiv site was “how to set up a referral program”, but I wanted to know if there is a content about the tactic behind a member get member strategy. Questions like “How many referrals one should give for receiving a promo code?”