Mike Lindell has to pay $5 million for losing his “Prove Mike Wrong” 2020 election challenge, an arbitration panel has ruled.

In a decision dated Wednesday, the panel found software developer Robert Zeidman had won Lindell’s 2021 contest challenging experts to prove that data he had was not from the 2020 election, and directed the MyPillow founder to pay him the reward money he’d promised in the next 30 days.

Lindell told NBC News on Thursday that the ruling was “a horrible, wrong decision.”

“It’s all going to end up in court,” he said.

The contest took place in August 2021 at a cyber symposium that Lindell — an outspoken election denier and conspiracy theorist — was hosting in Sioux Falls, South Dakota.

As part of the symposium, Lindell announced a contest called the “Prove Mike Wrong Challenge” in which participants were asked to find proof that his cyber data was not valid data from the November election, the ruling said. The announcement said: “For the people who find the evidence, 5 million is their reward.”

At a hearing in January, Lindell testified that the cyber experts he hired had convinced him that he “could not lose the contest because the data he had been provided was genuine election data,” according to the ruling, which was first reported by The Washington Post.

Among the attendees at the symposium was Zeidman, a Donald Trump voter who was excited to see the evidence Lindell had turned up.

Zeidman “wanted it to be 2020 election data,” said his attorney, Brian Glasser of Bailey & Glasser LLP. 

Zeidman “testified that he was interested in the claims that there had been interference in the 2020 election and wanted access to the data as promised to see ‘history in the making, perhaps to see an election overturned,’” the ruling said, and he decided to enter the contest because it was free, but “told his friends that he was unlikely to win because Mr. Lindell would not offer a $5 million prize if Mr. Lindell had not had his own experts vet all the data to be presented.”

But the “Red Team” of experts assembled by Lindell had their own concerns about the data, the ruling said, and members of the team “protested that the data was not at all what they expected.”

“They had expected to be provided with packet capture data that could be examined and authenticated to evaluate whether the data files provided were genuine or had been tampered with or altered,” the filing said. But that was not what they received.

One member of the team advised Lindell to call the contest off, but he refused, the filing said.

Zeidman was given 11 files to review in two days at the conference, and quickly changed his opinion about their merit.

“Much to his chagrin, he found it wasn’t 2020 election data,” Glasser said.

After analyzing the files, Zeidman believed he’d win the contest, the ruling said, and he then presented a report concluding that Lindell’s data “unequivocally” did not contain any information related to the November 2020 election, despite his claims that it did.

Lindell’s contest panel disagreed, so under the terms of the rules, Zeidman took the case to arbitration. Glasser said each side got to pick one arbitrator, who joined a third neutral arbitrator. All three ruled in favor Zeidman.

While Lindell was optimistic he could overturn the verdict in a federal court proceeding, Glasser said he and co-counsel Cary Joshi aren’t concerned.

“There are virtually no grounds to appeal an arbitration verdict,” Glasser said. “It’s just not going to happen.”

Lindell’s championing of election conspiracies have him facing other legal problems as well. He’s being sued by Dominion Voting Systems, a former Dominion employee named Eric Coomer and another voting company called Smartmatic for defamation over his election claims.

Still, Lindell maintained to NBC News that his theories are factual and, as he has said multiple times since the 2020 election, that he’d be showing evidence of his election claims in the near future.