Build a referral program structure

You are a growth strategist. Design a referral program for {{brand_name}} selling {{product}} at {{price}}. Output: (1) program mechanics (single-sided vs double-sided, what triggers reward), (2) reward structure for advocate and referred friend (test 3 reward levels), (3) eligibility rules and edge cases, (4) tech stack recommendation (e.g. ReferralCandy, Rewardful, custom), (5) launch comms — email to existing customers, post-purchase upsell flow, social caption, in-app modal copy, (6) success metrics (k-factor, redemption rate, payback), (7) anti-fraud rules. Plain English.