Why do you not need 在这里 here? Is it because 这里 is being interpreted/treated as a noun?
這裡 (zhe li) already means "here". Saying "at here" is redundant.
Exactly, we're not saying something is inside this place, instead the place itself is the acting subject of the sentence.
Should also allow "他们不收信用卡。“
这里 means here and 他们 means they. Duolingo really needs to fix their chinese lessons.
The given answer implies 'they'. I gave the same answer as AndersZhou1, which implies 'here'.