Hi @ink and thanks for reaching out!
Is that JSON object the exact configuration you used to create that user? I attempted through the Management API to create a user with those credentials and was given an error of improper JSON payload format.
However I did make a user with an ‘sms’ connection and was able to query the ‘/api/v2/users-by-email’ endpoint to get back my created user. The second endpoint I believe is the get a user which requires you provide the user id (with the connection prefix) in order to return the user. Do your logs reflect that a user was in fact created?
If you’d like, you can send me in a DM your tenant as well as the object you used to create the user so I can dig a bit more into this.