you can go with -2.08B if you can.
negative balance happen after long bidding war or multi-bid. Nordeus checks his balance only in 1st bid(ie with 5m you can bid and 10 player value 4m99 and if you sucess all you have -45m)
it's legal. he has 7 days for clear his debt. if he couldn't, his player will be automatically sold on tranfer liste one by one till he clear his debt.