I agree with marche.
I just tested it in Chelsea , but because of my apparel enhancements , my winnings are actually 1066 , not 900 as quoted as the prize
so , my balance was 934330 before going in to play , I take off 500 as entry fee, leaving 933830. I win my match and am awarded 1066, so my balance is now 934896
so in your case loser , when you win your winnings are actually 400 , but the award would be 900 , because the entry fee of 500 is taken off when you start the game.