Added into the odds section about this using the US odds system, not the European one. The US one works calculating the actual win amount + returning your initial investment. The European one only pays the win amount, keeping the initial investment.
In other words, if you enter odds 1.50:1, then for every dollar you bet, you get $1.50 + your initial dollar back. That is the winning odds.
European, if you enter odds 1.50:1, then for your dollar bet, you get back a total of $1.50.
Something to think about when now entering odds, as I only just noticed this returning initial investment + winnings.
So to pay 0.50 on every dollar, you would enter 50 / 100 into the odds for each outcome, so that for every dollar bet, the person gets back a total of $1.50. Being their initial investment of $1 + 0.50 win.