To automatically show commit messages in YouTrack on an integrated project in Bitbucket, you will need to set up a webhook in Bitbucket that sends notifications to YouTrack when a new commit is made. Here are the steps to do this:

  1. In YouTrack, go to the project that you want to integrate with Bitbucket and navigate to the Administration area.
  2. Under the Integrations section, select the Bitbucket option and enter the URL of your Bitbucket repository.
  3. Click the "Generate a new link" button to generate an integration token. Copy the token to your clipboard.
  4. In Bitbucket, go to the repository that you want to integrate with YouTrack and navigate to the Settings page.
  5. Under the Webhooks section, click the "Create webhook" button.
  6. Enter a name for the webhook, such as "YouTrack Integration".
  7. In the URL field, enter the URL for the YouTrack REST API. The URL should look like this: https://<your-youtrack-domain>/api/issues?fields=idReadable. Replace <your-youtrack-domain> with the domain name of your YouTrack instance.
  8. In the "POST Content" section, select "application/json".
  9. In the "Secret" field, enter the integration token that you copied from YouTrack.
  10. In the "Triggers" section, select "Push".
  11. Click the "Create" button to save the webhook.

With the webhook set up, YouTrack will automatically receive notifications whenever a new commit is made in the Bitbucket repository. The commit message will be added as a comment to the relevant issue in YouTrack, provided that the commit message includes the issue ID in the format #<issue-id>.