The rail panner app does not book reservations, it just forwards to some of the websites where you can do that.

For booking ferries, go to the ferry company website. Here is an overview of ferries with an Interrail  discount. Booking instructions on the individual ferry pages. There may also be other ferries; use Google.

Bitte beachten+denken: the longer the ferry, the higher the price. There are ALSO ferries (even many more) from further south in IT, like Bari or-best: Brindisi. Even without a discount the end price may well be lower as #2 with ´Rabatt´.ALL ferries currently charge quite high fuel-surcharges. There are at least a dozen sites that compare all ferries-use them to compare only, then book direct via your chosen one.

And also note that Igo has keine Bahnli-maybe utter surprise for the schwyzerli

Thank you for your both answers, either in English or in “Schwizertütch”.

Only French language missing !!!