While spinning the slot, my balance decreased by more than the bet amount.

You may be participating in the FOMO Jackpot.
By pressing the [OPT-IN] button in a jackpot-eligible game, the additional jackpot bet cost of USDT0.10, USDT0.50, or USDT1 (depending on your choice) will be deducted.
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You can stop at any time by pressing the [OPT-OUT] button at the bottom of the game.