It's die Schweiz and that phrase is indeed wrong. It must be
Vor allem in Deutschland, Österreich, der Schweiz und in Liechtenstein
That second in because the article breaks the row. Putting Liechtenstein in front of die Schweiz is uncommon. It's uncommon to take note of Liechtenstein at all, and they like it that way … for reasons. So,
Vor allem in Deutschland, Österreich, und der Schweiz
ich much more common, und sometimes referred to as
Vor allem im Raum D-A-CH
This uses the abbreviations of the International vehicle registration code.