Second, this is a max profit flat betting (sorry if I'm not correct on the max bet, but I can't publicly find PD limits).
It's weird from the screenshot how 3x pays out differently whether you roll hi or lo. He's winning 24 BTC when he rolls low, but only 23.99988 when he rolls high. Is this some kind of rounding error?
The "Over" Chance is actually 33.01000000000001%. I might have misplaced the first and last '1' but that's apparently where "Over 66.99" sits as opposed to the straight 33% that 'Under 33.00" is.