As far as I know, seat reservation is optional on all Enterprise trains. Turn up and go!
 

You can probably ignore what the app is telling you. They recently adjusted the timetable to double the number of trains running along this line, and some services are operated by different equipment - some from the north and some from the south. It may be that there’s a gremlin in the data.

I’m pretty sure that what’s happening is that it can’t find any seat reservations in second class (because of a data problem, rather than they’re all full), so it’s showing reservations in first class and telling you you can’t use them with your serving class pass. 
 

The ‘not included in second class pass’ message is unusual. And wrong, I think. I’m going to Tweet The Man in Seat61, and see if he knows!

I also see this message. It's complete nonsense AFAIK. Passes are valid in both classes.

​@Eurail Community Moderator could you please have this message removed?

What happens when you try to add one of the ‘forbidden’ trains to your trip?

If it lets you, and generates a QR code, you should be ok. If it doesn’t let you, you may need to contact customer services to get it resolved.
 

Last option would be to buy a ticket and keep the receipt, and send it in to Eurail for reimbursement. 

If it doesn't let you add the journey, you can always add it manually.

I’ve never posted in here before so not sure if this is the best way to thank you both in being so helpful so quickly !!! 

I’ve never had to manually add a journey so I'll try that first and see if it looks like it’ll work… otherwise on to customer support I suppose.

thank you thank you! 

Any reply is welcome! Many posters don’t even bother to acknowledge responses, sadly, so you already at the top of the class.

You can add a journey manually by scrolling to the bottom of the search results in the app where there’s a link.

Hi ​@rvdborgt, ​@Sage & ​@ralderton, you're absolutely right! It does seem strange and incorrect. We've forwarded this to the relevant department and anticipate that it will be reviewed and updated in our timetable.

Thank you for bringing this to our attention!