Mailchimp package not adding email address to list

I am using the following laravel package for my newsletters:

laravel-newsletter.

I have the following code in my newsletterController.php:

public function index() {
    Newsletter::subscribe('rincewind@discworld.com', ['FNAME'=>'Goti', 'LNAME'=>'Loki'], 'test');
    return 'Ola !';
}

Now when i go to: /newsletter in my application i see Ola !, but when i open my mailchimp dashboard i see don't see rincewind@discworld.com added to the list of emails for the list test.

I also tried the following method of the mailchimp package:

return Newsletter::isSubscribed('codedevakagautam@gmail.com');

This email address already exists in the list test, i get the following error:

Call to undefined method Spatie\Newsletter\Newsletter::isSubscribed() 

What am i doing wrong ? Can somebody please guide me.

via Chebli Mohamed