Reservation postal bus from Menaggio to St Moritz

We have Flex Swiss Travel Passes for 4 days in September, and plan to use them on the 631 route postal bus Sept 18 from Menaggio Italy to St Moritz. I went to the postauto.ch website to make seat reservations and it seemed to work (I have the booking number), but there was no request to pay for the reservation. Is this correct -- is the seat reservation free? I would hate to find out later that we lost our seats because we didn't know how to pay for them! Thank you for your help. We have been to Switzerland many times before, always using the wonderful trains, buses, and boats.

Welcome to MySwissAlps, ntnear!

I think you're referring to the Palm Express which has route number 90.631? Reservations are recommended indeed, but not charged as far as I can see. So I think you're all set now. If a surcharge still appears to be required, I expect you can just pay for it at the spot.

Thank you for confirming this, Annika. I can rest easier now!