Adding interest groups When creating new subsciber in Mailchimp API 3 - php

Question

Hoping for some help as can't find an answer anywhere.
I am using the following PHP function to add a subscriber to mailchimp. This works fine. What I need to do is add the user with one or more group interests assigned. So for example I have a Group named "Test Group" which contains two interests "Test 1" and "Test 2". How would I amend the below function to include 1 or more interest values?
function mc_subscribe($email, $fname, $lname, $apikey, $listid, $server) {
$auth = base64_encode( 'user:'.$apikey );
$data = array(
'apikey' => $apikey,
'email_address' => $email,
'status' => 'subscribed',
'merge_fields' => array(
'FNAME' => $fname,
'LNAME' => $lname
)
);
$json_data = json_encode($data);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'https://'.$server.'api.mailchimp.com/3.0/lists/'.$listid.'/members/');
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json',
'Authorization: Basic '.$auth));
curl_setopt($ch, CURLOPT_USERAGENT, 'PHP-MCAPI/2.0');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POSTFIELDS, $json_data);
$result = curl_exec($ch);
return $result;
};

Answer 1

The documentation contains enough information to figure this out, even though it doesn't say so directly.
You'll need to add an interests object to your request. It should take interest IDs as keys and boolean values as false. So you could update your code above as follows:
$data = array(
'email_address' => $email,
'status' => 'subscribed',
'merge_fields' => array(
'FNAME' => $fname,
'LNAME' => $lname
),
'interests' => array(
'9143cf3bd1': true
)
);
Note that you'll need to get the IDs from the API, as there's no way to collect them from the web app, and also you should remove the apikey element from your request it is no longer used.