Some Pokémon Go Fest attendees are filing a lawsuit against developer Niantic. The attendees are seeking travel reimbursement since Niantic wasn’t able to deliver on its promises when the Pokémon Go Fest turned out to be a disaster.

Chicago-based attorney Thomas Zimmerman said that he was contacted by Jonathan Norton, a “Pokémon Go” player from California who travelled all the way to Chicago for Niantic’s event this past weekend. Zimmerman says that “20 or 30” other players have joined the class-action suit, as first reported by Polygon.

When Norton and many others arrived in Chicago for the Pokémon Go Fest, the game was simply not working. Niantic promised that the festival would give attendees the chance to capture rare Pokémon, but that wasn’t the case as everyone was unable to connect to the game.

READ: ‘Pokémon Go’ Legendaries Update: Moltres, Zapdos Release Dates Announced After Disastrous Fest

Niantic offered refunds to attendees who asked for it later that afternoon, while everyone at the festival were given $100 worth of PokéCoins. However, Zimmerman said that what Niantic has offered was simply not enough.

“We’re not seeking any relief with respect to the failure to get legendary Pokémon, because Niantic is offering that,” Zimmerman said. “But Niantic is not offering to refund people’s travel expenses for coming to Chicago. Most of the people came from out of state, many people from other countries — I talked to someone who flew in from Japan.”

His clients are asking for the amount of money that they’ve spent to travel to Chicago just to participate in the Pokémon Go Fest. Zimmerman also stated that Niantic made “promises that were not kept” when it comes to the type of experience that his clients were expecting.

Niantic also extended the amount of time and locations where rare Pokémon could be caught around the Chicago area. The company also promised that all attendees would receive Legendary Pokémon in their accounts. Despite all of this, it does look like many are still unhappy with what happened during the big event.

Earlier this week, Niantic CEO John Hanke published a lengthy blog post apologizing to fans. Hanke also took the time to explain what happened at the Pokémon Go Fest, blaming the cellular data congestion during the event.

READ: ‘Pokémon Go’ In-Game Bonuses Extended After Chicago Event Fiasco​

“Technical issues with our game software caused client crashes and interfered with gameplay for some users. The gameplay issue was resolved with a server configuration change and the crashes were also addressed for many but not all users,” Hanke explained.

“A more protracted problem was caused by over-saturation of the mobile data networks of some network providers. This caused many attendees to be unable to access ‘Pokémon Go’ or other Internet services. Network congestion also led to a login issue which affected some users able to access the Internet,” he added.