No, it is not possible to convert madpoints into credits. Madpoints are used to order Prizes in the Prizes tab.
Madpoints can be obtained through free games or the use of credits in paid games. Often, you can have many more madpoints with games where the use of credits is mandatory.
For example, you can use your credits for tournaments where you can have a lot of madpoints without being first. But under no circumstances can credits be used to order Prizes.
