Breakdown of На кассе самообслуживания я случайно пробила купон два раза и попросила кассира помочь.
Questions & Answers about На кассе самообслуживания я случайно пробила купон два раза и попросила кассира помочь.
На is used with places understood as a point/spot where an action happens (a station, a desk, a counter, a checkout): на кассе, на почте, на стойке регистрации.
В would sound like inside a physical container, which a checkout isn’t.
It’s prepositional case (singular) after на meaning location.
касса → (на) кассе is a standard spelling change for many feminine nouns ending in -а: школа → в школе, касса → на кассе.
самообслуживания is genitive singular. It means “of self-service,” so the phrase literally is checkout (of) self-service = “self-checkout.”
This is very common in Russian: отдел игрушек (toy department), зал ожидания (waiting hall), касса самообслуживания.