Hi Peter, I'm not using a short code, I'm using the MB 'Registration Form' element within Bricks. However, I figured it out, Bricksforge makes the Roles available within the form element, so it was easier to select.
However, the issue was with SureMembers and NOT Metabox, they have the WP Role value set as 'suremembers_recruiter'.
So, with it displayed everywhere as just 'Recruiter' or 'Candidate', I wrongly assumed it was that but all lowercase. I have now changed it accordingly in the MB Profile Form element on the Registration Form page in Bricks.
Now it is working.
Thanks for the suggestion though, I appreciate you replying.