Invitations
Allows repository administrators to send email invitations to grant read, write, or admin privileges to a repository.
Prepare:
$invitation = new Bitbucket\API\Invitations();
$invitation->setCredentials( new Bitbucket\API\Authentication\Basic($bb_user, $bb_pass) );
Send invitation:
$invitation->send($account_name, $repo_slug, 'user@example.com', 'read');