There isn’t a minimum wager when playing online. If you want to bet $1 or even 50 cents on a “jackpot” parlay, go for it.
There IS, on the other hand, a maximum wager – but it’s challenging to quantify. A well-respected, loyal customer might be able to get down as much as they want on a game, but it’s safe to assume amount in the high-four figures ($5,000 or more) might require special permission.