[Edit, this is not correct: If you have an Interrail for Germany, then it is not valid outside of Germany. For the train shown, you'll need an additional ticket from Bologna to Kufstein. From Kufstein, your Interrail pass for Germany will be valid. You can book via bahn.de, oebb.at and trenitalia.com. They don't necessarily give the same prices so compare.]

A reservation on this train is not obligatory (that's a bug in the app) but very much recommended during the summer because it's very busy.

Hi! Thank you for your answer and the suggestions.

I’m just a little bit confused because here there was written that the connection was included in the pass:

https://www.interrail.eu/en/interrail-passes/german-rail-pass

My apologies! I completely forgot that the Interrail for Germany is also valid in a few trains outside of Germany. So this looks like a bug in the app. Do you have the latest version? There was an app update yesterday so that might also solve it.

In any case, there's a 10 EUR Interrail supplement, which you can buy on the train or in advance via https://tickets.oebb.at/ and an optional (but highly recommended) reservation of 3 EUR that you can buy on the same website.

Hi both, the information has been forwarded to the relevant teams to check it and adjust accordingly. It is indeed covered as mentioned on the website. I advise you to make use of the alternative ways of booking like suggested by rvdborgt. Cheers, 

Ok, thank you both for the help!!
Have a great summer!