How do you hand out promo codes and license keys today?

Keydrop launches here tomorrow (Nov 9). Before that, I'd love to learn how other makers do this.

When you give out App Store promo codes, discount codes or license keys, what do you use? A spreadsheet, Gumroad, Lemon Squeezy, your own script? What is the most annoying part: tracking who got which code, codes leaking, refunds, or something else?

Your answers will shape what I build next. Thanks!