MySQL Insert query failing

I'm using backand.com to make a query that attempts to create a record in a users table if the email isn't already used:

INSERT INTO users (email, firstName, lastName, password)
SELECT * FROM (SELECT '{{email}}', 'test', 'person', '{{password}}') AS tmp
WHERE NOT EXISTS (
    SELECT email FROM users WHERE email = '{{email}}'
) LIMIT 1;

It validates, but when I run it with params:

email: dave@gmail.com
password: test

I get the error:

An error occurred, please try again or contact the administrator. Error details: Duplicate column name 'test'

Why is this failing? I don't get it.

Thanks.