I am getting the same error trying to link my Bitbucket repo. I am using docker-compose and the error I extracted from the log indicates that credentials with repository write permissions are required:
ERROR:rasax.community.api.blueprints.git:Given repository credentials don’t provide write permissions to the repository. Please make sure the ssh key is correct and the administrator of the remote repository gave you the required permissions.
Unfortunately, the Rasa X docs only suggest to use an Access key, but Bitbucket Access keys provide just read-only access.
Not sure how this can be solved with Rasa X since it seems that only users with associated emails can have also write access.