The Bitbucket posting user must be created by an individual on your team with the following administrative permissions:
A PullRequest account with an Owner role for the organization in question.
An Admin role on your Bitbucket Server instance.
Log into the PullRequest Proxy and click the Configure Bitbucket button on the home page.
Paste the root URL of your Bitbucket Server instance (this will be whatever domain your team usually uses to access Bitbucket). Example:
Log in to your Bitbucket instance as an admin and create a new user with the username PullRequest. This will be the user that posts comments in your repositories.
Add the PullRequest user to all of the repositories you want code review on. Be sure to grant the user WRITE permission so it's able to post comments.
Log in to Bitbucket as the PullRequest user.
Create a personal access token for the PullRequest user in Bitbucket by opening https://our-bitbucket.internal/plugins/servlet/access-tokens/manage in the browser you were logged into as the PullRequest user.
The access token will need to have Projects READ and Repositories WRITE permissions.
Once generated, copy the personal access token to your clipboard and go back to the PullRequest Proxy UI with the Bitbucket Settings modal open.
Enter PullRequest as the PullRequest Username (or whatever name was used in Bitbucket).
Paste the personal access token into the modal and click Update.
Open the Repositories tab in the left sidebar. The repositories the PullRequest Bitbucket user were added to should appear in a list here.