I think I just found a bug. I opened the page, the game entered "demo mode", and I entered 0.01 for the bet and a 80% chance of winning. The "if I win I will receive" box changed to 0,0123. When I click the Spin button, I get the following JavaScript alert:
There was an error (invalid parameters: winnings not equal 0.0123 0.0122625!), please check your input is valid. The wheel will now be reset.
EDIT: if you touch the last text box (for example by adding a zero), the winning chance box gets updated and one can play.