Was zum Teufel soll ich mit dieser beschissenen DB-App machen und gibt es eine andere Möglichkeit, ein 58-Euro-Abonnement zu kaufen?

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Try via the website or your local regional provider?

!49

A lot of companies. You might, for example, want to check your local company.

For example, my local company runs several actions ever year where you get reduced cinema tickets or reduced admission to the amusement pool or such.

Also they offer it as physical card, which avoids all those pesky app issues.