Why "tại" and not "ở"
I used ở and it was accepted
is it correct if change tại into ở ?
Explanation for ở and tại
But it doesn't include this case. This says that they are both interchangeable, save tại can't be used after 'to be'.
So this needs to include ở, as everyone else says.
Tại doesn't make sense in this sentence.