Email Already Registered
Use a different email, or look up the existing user if you meant to update that one.
An HTTP 409 application/problem+json response:
{
"type": "https://problems.atlas.propertyfinder.com/users-email-taken/",
"title": "Email Already Registered",
"status": 409,
"code": "users_email-taken",
"detail": "A user with this email already exists."
}