It's a subscription requiring a German bank account in most cases. In theory any SEPA account should work, but it's a well-known problem that sellers break the law and accept only domestic accounts.
However, reportedly a small number of apps allow paying by credit card. And some are more flexible regarding cancelling the subscription than others.
App stores are not global. I remember someone saying a certain D-Ticket app not being available in their country. I vaguely remember you can switch the country, but it's a hassle and can cause problems with other apps you have. Another barrier to keep in mind besides the payment method.
However, reportedly a small number of apps allow paying by credit card. And some are more flexible regarding cancelling the subscription than others.