draftkings promo bet hit but only paid bonus credit instead of cash

put in a promo bet on an nba underdog last night and it actually hit, but when i checked after the game the payout came through as site credit, not cash. was kinda thinking if you win, you get real money, not just more bonus bucks to try and run it up again. is this normal for promo bets? do they ever pay cash or is it always credit with these things? i don't mess with promos much, usually just stick to slots or live dealer, so i'm not sure. anyone else get hit with this before, or did i mess up somewhere?