Munich to Maienfeld

Did you check Deutsche Bahn website?

Ester, I visit friends in Maienfeld at least once a year and can't say enough wonderful things about the village and the kind people there. I usually just take the train from Zürich which stops in Sargans for a couple of minutes...just enough time to change to the nearby track.
My favorite hotel is the Heidihof Hotel with an amazing view, fantastic restaurant, wonderful breakfast and the most caring, sweet staff. It's just a bit of a walk into town but just down the path to the Heidi House. The Swiss Heidi Hotel is closer to the train station, with the same fantastic breakfast, view and people but is more of a business hotel. I've stayed there numerous times as well.
The Deutsch Bahn will give you all the info you need to get to Zürich or the sbb.ch/en will also give you the info to get all the way to Maienfeld. Be sure to purchase a roundtrip ticket from Zürich to Maiefeld because the "station" in Maiefeld doesn't sell tickets.

OP will also find full end-to-end connection on DB website.

Thank you for the helpful information!
I checked the DB page. There is an option that takes us to St. Margrethen, then to Sargans and to Maienfeld. But we are not returning that way as we continue to Geneve.
We would need to go on to Zurich. And now we know that we cannot buy a ticket from Maienfeld to Zurich.
The BD page does not allow me to reserve tickets online. Would it be safe to wait until the day of travel to purchase those tickets?

The BD page does not allow me to reserve tickets online. Would it be safe to wait until the day of travel to purchase those tickets?

The DB cannot sell tickets for that train connection since it implies trains of three different national carriers (DB, ÖBB, SBB). You can book however at trainline.com, where you also can book the cheaper connection using the IC bus via Zürich (random day in April: EC / IC / S via Innsbruck = €69; Bus / IC / S via Zürich = €32). Book your ticket from Maienfeld to Zürich at www.sbb.ch or buy from a vending machine on the spot (afaik there is no reduction for early booking on that leg).

PS.
1. the train connection would bee bookable at sbb.ch too, but for hefty CHF 100 (= €90).
2. For the bus connection you may save money if you split up your booking: (1) IC bus Munich-Zürich at the operators website (www.bahn.com) - early booking prices usually €19.90. (2) Swiss S-Bahn ticket Zürich - Maienfeld at www.sbb.ch - CHF 34 (~ €30) or CHF 17 with half fare card..