First, you will need to install the Behave Pro for Bitbucket plugin into your Bitbucket instance. This plugin is needed in order for Behave Pro for Jira to communicate properly. You can download the Behave Pro for Bitbucket plugin from the link below.
Note: There is no license needed for the Behave Pro for Bitbucket plugin.
After you have installed it in your Bitbucket instance, you will need to set up the application links between Jira and Bitbucket. (You can read more about the Atlassian application links here: https://confluence.atlassian.com/doc/linking-to-another-application-360677690.html)
To set up the application links, first navigate to the Administration admin page of your Jira instance and click "Application Links" on the left navigation menu. You will need to fill in the base url of your Bitbucket instance.
Next, you will be prompted with the following dialog. Make sure you select the "The servers have the same set of users and usernames" checkbox! The git integration will not work without this!
After clicking "Continue" you will be redirected to the Bitbucket instance, simply select "Continue" again and you will be redirected back to the Jira.
After that, your application link should show a green "Connected" status.
That's all. You are now able to use git integration for this Bitbucket instance from any of your Jira projects. You can continue by reading the following documentation in order to set up a Jira project: Connecting Bitbucket to a Jira project