A few comments...
First anyone who plays matchplay challenge for credits is crazy. You are risking 100 to get a 80 payback, that is a 20% rake, Vegas only takes a 10% rake on the loser. You bet $100 in Vegas you give them $110, if you lose they keep it all, if you win you get back $210. The problem is this should not be a gambling site and I can't believe they are allowing it...legal problems on the way.
Second if they are allowing gambling, because it is that, not buying credits. If I put in 10,000 credits to gamble with then I should be able to retrieve my winnings. The credits are not just to buy equipment when they change it to gambling.