How to create a blog post comment using rest api with content url ?

Are you using OAuth authentication?  That is a requirement to use ContentUrl.  You specify the content url that is being commented on. It is used to allow comments to be made against an external Url outside of community.

Thanks, 

Yes, I am using OAuth,

Steps:

1. Created a blog post from that we can get the content id, content type id, and URL

2. I am using that URL to create a comment which allows me to create a comment by using rest API. But the thing is, it is not visible in Dynamics UI. And Next one is when I create comments from dynamics UI, That comment is not able to get from comment list API by using CONTENTURL.

When you create a comment, are you getting a populated Comment entity returned in the Rest Response?  Are there any errors or warnings returned in the Rest Response?

If that portion is working and you have a created comment, when you list the comments by ContentUrl what do you get back in the response?  A list of 0 comments?  Any Errors returned in the Rest Response?  Any exceptions in the exception log? 

When you create a comment, are you getting a populated Comment entity returned in the Rest Response?  Are there any errors or warnings returned in the Rest Response?

If that portion is working and you have a created comment, when you list the comments by ContentUrl what do you get back in the response?  A list of 0 comments?  Any Errors returned in the Rest Response?  Any exceptions in the exception log?