If you are looking for a solution to the problem that no Sparkassen girocards can currently be added to Apple Pay, you have found it. And it is also simple.
If you get the error 9010 or 9050 after you have activated the Sparkasse card in the Push TAN app, then the following trick will help: Simply turn off WLAN and Bluetooth on the iPhone and go through the whole procedure again. With LTE as the only data connection, the chance is very high that the activation of the card (or digitization as the Sparkasse calls it) will be completed successfully.
So you can finally set up your new iPhone completely.