can anyone explain this?? I have NO IDEA what a "double spend" is ??

https://directbet.eu/BetStatus.cshtml?BetID=14dsZ5azoAQXgjkxgkXL8we6VG5BjdJpdh

"You have Three of a kind, Jack's against One pair, Queen. A Payout of 0.1709 BTC was used to cover unpaid losing bets 1GJfAJ3uD7h4Vr8Z3SQqu4x6Ygz2zGXwPn and 19FjAnt8an6jDaZN2mTqrca4Hj4iA6KkBa that were double spent."

I won, why didn't I get paid??