Error checking pages

This only means that some request to check a page failed.
Maybe WP reportd some of those page as available but then the the request failed for some reason.
So some other page was checked instead and the status is still displayed normally.

Nothing to worry about.

Thanks for the fast reply
Please let me know how to fix this because I want to know where can my theme place the ads in posts

Actually nothing to fix.

The report on the screenshot already shows available positions.

You can also use debugging funaction Show positions:
https://adinserter.pro/documentation/debugging

But the green circle doesn’t show in posts column

In such case use debugging funaction Show positions.

It will show available positions on any page or post.