QR on a brick wall outside a secret bar. A password you rotate daily, plus a 40-scan cap: past the cap the code stops resolving and late arrivals get the limit notice.
You set the password in the panel and change it each day, handing the new one to guests over Telegram. The 40-scan limit does the capacity control on its own: once 40 people have passed the gate the code stops resolving for everybody, so nobody has to stand at the door counting.
Free tier includes 1 standard QR code. Upgrade to the paid Eternal tier for blockchain permanence and the recovery key.