How do bracelets work with which you can pay at events?

Question

Bluetooth

Many events are now introducing a bracelet system.
These bracelets are a pass to the event area, and you can also pay from them, tell us what technologies are used to organize such a system

Answer 1

RFID tag and database in which everything is stored, incl. balance.

Answer 2

The AFP just has an Alpha debit card inserted in the bracelet, it has the full number and expiration date. Payment, respectively, paypass. Therefore, you can pay for everything at the festival with any card with a paypass.
On Tomorrowland, the bracelet is more cunning, it seems like RFID with a sewn-in ID, the same ID and pin for it are printed on the bracelet strap. You link the ID of the bracelet to your account using a pin, you already make a balance replenishment to your account. https://blog.adafruit.com/2014/11/19/tomorrowland-...

Answer 3

As already mentioned - RFID.
By the way, they describe their experience at the Ukrainian festival Atlas Weekend - google it, maybe you will find more detailed descriptions
https://www.imena.ua/blog/atlas-weekend-pay-talks/