When I try to initiate a build for the PR request, it shows

Looking up MI/apis for branches
Checking branch master from MI/apis
Met criteria
Looking up MI/apis for pull requests
Checking PR from ~ABISHEK_MANOHARAN/apis and branch master
Does not meet criteria

Now, the credentials used in Jenkins for Bitbucket does not have permission to read "~ABISHEK_MANOHARAN/apis" repository, but it has the permissions to read/write on "MI/apis" repository.

It's not possible to provide the credentials read access to all the repositories from which a pull request might come.

Using the credentials I am able to view and approve the PR on the Bitbucket Server Web interface, so I think it should be possible to build with the PR from Jenkins as well.

If, I give read access to "~ABISHEK_MANOHARAN/apis" repo, then it's building fine.