Moodle Plugins directory: Enrolment key based self-registration | Moodle.org

Enrolment key based self-registration
Moodle Enrolment key based self-registration
This is a functional clone of the Email-based self-registration plugin that also enrols a user into available courses based on a token supplied. When a user enters a valid token it will automatically enrol them into the course that token was specified for.
Courses that provide self enrolment can restrict access to them with a key. If the signup token matches any course enrolment key then the new user will be enrolled into those courses.
Courses that
provide self enrolment can restrict access to them with a key. If the
signup key matches any course enrolment key then the new user will be
enrolled into those courses.
The streamlined process flow:
(Signup page -> Course)
The normal self registration process flow:
(Signup page -> Confirmation page -> Open email client and click link -> Navigate to course -> Click on enrol -> Enter enrolment key -> Course)
i have installed this plugin on my 3.5 version and the course is live but when new users try to create an account and enter the enrolment key it keeps showing 'The enrolment key you have entered is invalid' i have changed it and ensured that it is the same yet it keeps returning this error... any idea's?
and install VERSION3, it works with later versions of Moodle.
Are there plans for a 4.x version or or even a schedule?
Thank you!