Mark the member as a referral of another member of the same project. Identify the referrer with exactly one of referral_code (the referrer's permanent referral code, shown as support_id in the member profile) or referrer_id (the referrer's member UUID).

The referral loyalty mechanic must be enabled for the project. A member can have only one referrer: the call fails when a referrer is already assigned, and self-referral is rejected. On success the referred member receives the configured referral reward, and the referrer reward is scheduled when the mechanic postpones it by registration date and the member is already verified.