Thank you for sharing the Hub ID, @Sabita_Sahoo.
I am able to successfully retrieve data for the "News" blog and its sole blog post at this time.
To pull the one blog post through this endpoint, I used:
But it also worked with:
and other variations I tried.
Here is some of the data returned:
author_at:1544611978071 (December 12, 2018, 5:52:58am UTC-05:00),
I could also retrieve this single blog post via this endpoint using:
The request URL you are using is correct, and there doesn't appear to be an issue with the endpoint, since I can retrieve the data successfully. Are you certain you are using the correct API key? For reference, it is accessible here.