If you have a paypal account you can link your bank account the paypal account.
Paying per direct debit did not work for me. (I am also from germany)
You can transfer money from the bank account to your paypal account (Takes a couple of days).
Now you can buy anything you want from Impulse as long as there is enough money on the paypal account. It's like a prepaid option.
With this method I bought Sins and Entrenchment.
