The biggest jackpot payout happened in 2018 when a lucky player hit the Mega Moolah progressive jackpot. He won a jaw-dropping €18,915,872.81 prize while playing the legendary slot on his phone. The player's identity remains unknown, but we do know that the casino in question was Grand Mondial Casino. Before this amazing win, the record was the €17.8 million win from 2015 which set the Guinness World Record for the largest jackpot payout in an online slot machine.