I see APIs for adding comments and label for issues.
There is an API to post comment on pull request with file name as input.
I am looking for some API using which I can add label and comment on to the Pull Request just by having Pull Request number (just not specific to commit, file or line number)
I would appreciate if you point out to any such APIs.
From the documentation:
The Issue Comments API supports listing, viewing, editing, and creating comments on issues and pull requests.
So use the standard API for creating a comment.
I hope that helps!