From Athens to Kiato - Seat reservations

Hello,

I'm looking at the routes from Athens to Kiato by train (with the interrail pass).
When I add the train in the Rail Planner application, I realise that I can't book the ticket, it only says "no reservation" when I click on "show services".
Does this mean that I don't need to book a ticket and simply activate it as a journey on the application?

Thanks in advance