What pass you ahve does not matter.

It can mean anything-as you describe and also that their system is unable to contact original selling place/railway or that thee are other hicups.

Again: forget that app, use other ways-as detailed by seewulf on a separate page, directly by railways. Cheaper too and much more chance on succes. It will also tell you when it has to be done elsewhere-do not assume that each&every obscure train is even online-to the utter surprise of today´s youth who cannot even think of the possibility that some things are not on their fone!

The advice from the experienced travellers in the community is to use other ways to make reservations than the Interrail/Eurail website. You can look at the guide in the link:

https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105

If you, after having looked at the guide, have questions about how to make specific reservation, please give your travel details (departure date, time and route) preferably in a new post, and you will get advice. 

If this is in the app, then it just doesn't know the price for some reason. But be warned: the prices it does quote are not always correct.