Mailchimp grouping doesn't seem to work - php

Question

I am trying to implement an opt-in on a website to add a newly registered user to a mailing list on Mailchimp. This user can either be an individual or a business client and has to be in different groups.
Now what I've done is, I created 1 list with 1 group and in that group I created 2 subgroups(?)
Like there's a group title and there's groupings underneath. Now I try to use the API Wrapper provided over here: https://github.com/drewm/mailchimp-api/ and used this method for the API request:
$r = $mailchimp->call('lists/subscribe', array(
'id' => 'REMOVED_ID',
'email' => array(
'email' => 'REMOVED_EMAIL'
),
'merge_vars' => array(
'groupings' => array(
'id' => REMOVED_ID,
'groups' => array('REMOVED_NAME')
)
)
));
For obvious reasons I've replaced the actual values with placeholders.
What happens is: The user with the opt-in gets a email asking for their confirmation, and then the email adres gets added to the list but they're not in any groups.
Am I doing something wrong or am I being impatient?

Answer 1

I've found out what the problem is for this particulair problem. The JSON produced by the MailChimp class looks like this:
{"id":"ID_REMOVED","email":{"email":"EMAIL_REMOVED"},"merge_vars":{"FNAME":"Captain","LNAME":"Jack","groupings":{"id":ID_REMOVED,"groups":["GROUP_NAME_REMOVED"]}},"apikey":"API_KEY_REMOVED"}
But it should have [] around the groupings like so:
"groupings":[{"id":ID_REMOVED,"groups":["GROUP_NAME_REMOVED"]}]
Now I don't know how to achieve this, but for future reference, this is what caused my problem