A major Pokemon Go festival in Chicago to celebrate the one-year anniversary of the virtual game went badly wrong when technical glitches prevented many fans from logging on.
The problems forced Niantic, the developer of the wildly popular augmented reality game, to promise that everyone who registered for the event would get a full refund for the $20 (€17.10) tickets and $100 (€85.70) in credits for use of the app.
Niantic chief executive John Hanke was booed when he took the stage at Chicago's Grant Park to address the thousands of frustrated Pokemon enthusiasts.
Some in attendance had paid as much as $400 (€342.80) online for the tickets, which sold out within minutes of their June release.
While no official attendance figures were available, organisers had planned for as many as 20,000 Pokemon players and "trainers" at the festival billed by Niantic as the first official anniversary event in the world.
John Haberkorn of Chicago, a member of the Official Pokemon Go 40 Club, an international online community of high-level players, said he started queuing for the opening of the festival at 6am.
"The excitement has just been drastically minimised because of what we've experienced today," he told the Chicago Tribune.
Late in the day, Niantic's chief marketing officer Mike Quigley tried to placate irritated players by announcing that everyone who scanned a code when they entered the park would automatically receive the Legendary Pokemon Lugia, a rare and powerful creature difficult to defeat in virtual battle and prized by Pokemon enthusiasts.
Niantic says Pokemon Go has been downloaded 750 million times since it was launched. The augmented reality game that uses GPS to locate, capture, battle and train virtual creatures was introduced in the US in July 2016.