These are user to user forums, not Magix Support so no-one here can directly help you!
However, it seems, from the error message, that your payment method is being declined or is failing for some reason. Depending where you are in the world, this could be a problem created by your browser. Have you tried to use a different browser?
If you still cannot complete the payment and assuming you have a Magix account already you could go to this page, log in and raise a support ticket with the Sales Team.