Public requires a direct, personal relationship with anyone you refer, and bars sharing your link by advertising or similar means.
What the clause says
Public's referral terms state that you may only refer people with whom you have a direct, personal relationship, and that you may not share your referral link or otherwise solicit anyone through spamming, commercial advertising, or other similar means. A separate sentence limits the program to personal use and says it may not be used for commercial purposes.
Keep two rules apart
Public separately says you agree not to sell referral codes or create websites, email addresses, or social media using Public's name, images, or content. That is a trademark and impersonation rule, not a posting rule. The personal-relationship clause is the one that governs where a link may go.
The cap has no clock
Public caps rewards at $500 across all promotions on the app, with no calendar year or rolling window attached. Once you reach it you are no longer eligible for any reward program, though your referral link keeps working. At $20 a referral that is roughly 25 referrals, and it is effectively a lifetime ceiling rather than an annual one.