Search query redirect to page

How did you add that redirect? To get that result indicates the redirect is incorrect.

Source: ?s=awesome
target: /postA

That was what I added.

Are there any warnings when creating or editing that redirect?

No, none

There are when I use the same the source URL.

Did you enable the regex option?

When I activate regex it shows this
To prevent a greedy regular expression you can use ^ to anchor it to the start of the URL. For example: ^/?s=awesome