Please don't use the rail planner app to plan. It is only updated about once per month. The best is to use national websites (such as www.trenitalia.com for Italy). For international planning, the DB planner (or DB Navigator app) is good. It has about the same coverage as the rail planner app but is updated twice/week and therefore much more up to date.

I suspect that Trenitalia are still not finished with their summer timetables, so you may want to wait with reservations for a bit, at least until next month. Pass holder seats within Italy are not quota-controlled so availability is usually good.

Many thanks for your response. Ok so I am confused now as I thought to put a trip on your pass you have to have it on the rail planner app? Or is this not necessary? Reading the interail advice it guided me to the app. This is really confusing. Any advice with that? Thanks again.

Yes, before you board a train, you need to add a journey to My Trip and then to My Pass. And by the time you'll be taking the train, the timetable in the app will normally have been updated.

But for planning purposes, the app is not reliable enough because it gets too few updates. For Italy, www.trenitalia.com is much more up to date and complete.

Many thanks for your response. May I ask one more question. I have found that two of the train journeys match up on the interail planner and reservation site. Do you think it is ok to go ahead and book those ones? It will make me feel better if I know that I am making headway with my trip. Many thanks.

The reservation website will be more up to the than the app. I only use the app to add the trains I use, not for planning because it's not reliable.

By the way, to book day trains in Italy, it's cheaper to use the ÖBB website (using these steps) because then there are no booking fees (Interrail charges an extra 2€ per person and train).