The meaning and parsing of “はっといた”

Question

In the Kanzen Master N2 listening textbook, there's the following sentence:

女：　昨日、はっといたんだけど。

Of which in the answers the correct reply was specified as:

男：　その壁に？
Man: On that wall? (?)

But I'm not sure what the first sentence means or how to break it up, let alone why that's the answer.

What exactly does the first sentence mean? Is it はっと + いた to mean "I was taken aback"? If so, why would it be done on a wall or is that some kind of an expression, e.g. "Because of that obstacle/barrier"?

Answer 1

Sounds like I put it [the notice/schedule?] up on the wall [for all to see?] yesterday.

spaceALC:

～を壁に貼る stick ~ up on the wall

Apple dictionary:

ポスターを壁にはった｜We put up posters on the walls.