I have tried multiple times, and checked with my bank - there is nothing wrong with my card - but your payment system rejects the payment details on it as invalid.
. . . . but your payment system rejects the payment details on it as invalid. . . . .
This is a public user to user forum provided by Magix, it is not Magix Support so is not our payment system.
For payments your bank must support 2 factor authentication - see this comment from Magix, additionally some types of Debit card may not be accepted as a valid payment method - eg prepaid cards.