Did you get it working in the Sparkasse app? A while back I wasn’t able to set it up because it required a secure lockscreen on Android.
On January 3rd of this year, with the help of this forum post I was able to set up said secure lockscreen:
But still, Sparkasse can’t complete Wero setup because showing the initial PIN entry window doesn’t work (for Delta Chat it does when adding a new device, so no Sailfish OS issue)