Do I need to pay twice on iPad and iPhone?

I purchased the upgrade to DTTG3 on my iPad and it seems to work fine. But on my iPhone DTTG3 wants me to buy the app again.
What am I doing wrong? Or is your intention to get paid twice on iPad and iPhone?

This isn’t necessary. Or do you use different App Store accounts on both devices?

No. It is the same app store account. Maybe It should delete and install the app again on the iPhone?

A screenshot of the available options on the iPhone would be great, thanks.

Can you scroll down further on that screen?

Interesting … I didn’t recognize “Wiederholen / Wiederherstellen”.
Should I try this?

Yes, this should restore the purchase from the iPad.

That’s it. Thank you for the quick help!