The article goes into that. If you open up the app ahead of time and download th...

shaftway 4 months ago | parent | context | favorite | on: Reverse engineering Ticketmaster's rotating barcod...

The article goes into that. If you open up the app ahead of time and download the ticket, it gets enough information to re-generate the barcode every 15 minutes. It's only a problem if you don't go into the app and fetch the data ahead of time.