Many thanks for the reply Falco. Specifically using curl exactly as you suggest I get a ‘You are being redirected’ response that would send me back to the home page. No login email is triggered. I was getting a similar result with the tool I was using - which was following the redirect back to the home page.
I don’t want to use DiscourseConnect as the only required login after signup is for Discourse.
Just also to add that, as a long-time user (and admirer) of Discourse forums this is my first foray into the other side - and the API / webhooks are just great; really easy to work with and very powerful.