Cannot create campaign Mailchimp API 3.0 - PHP
<p>I'm trying to integrate the MailChimp API 3.0 with PHP into a custom built CMS. When I try to create a single campaign with the following code I have an error message.</p>

<h2>CODE:</h2>

<pre><code>$apikey = &lt;--api-key--&gt;;
$list_id = &lt;--list-id--&gt;;

use \DrewM\MailChimp\MailChimp;

$MailChimp = new MailChimp($apikey);

$result = $MailChimp-&gt;post("campaigns", [
                'type'              =&gt; 'regular',
                'recipients'        =&gt; ['list_id'           =&gt;  '$list_id'],
                'settings'          =&gt; ['subject_line'      =&gt;  'test subject', 
                                        'reply_to'          =&gt;  'test@test.com',
                                        'from_name'         =&gt;  'test name'],

            ]);

echo "&lt;pre&gt;";
print_r($result);
print_r($MailChimp-&gt;getLastRequest());
echo "&lt;/pre&gt;";
</code></pre>

<h2>ERROR MESSAGE:</h2>

<pre><code>Array
(
[type] =&gt; http://developer.mailchimp.com/documentation/mailchimp/guides/error-glossary/
[title] =&gt; Invalid Resource
[status] =&gt; 400
[detail] =&gt; The resource submitted could not be validated. For field-specific details, see the 'errors' array.
[instance] =&gt; 
[errors] =&gt; Array
    (
        [0] =&gt; Array
            (
                [field] =&gt; 
                [message] =&gt; Schema describes object, NULL found instead
            )

    )

)
</code></pre>

<h2>USING <code>print_r($MailChimp-&gt;getLastRequest());</code></h2>

<pre><code>Array
(
[method] =&gt; post
[path] =&gt; campaigns
[url] =&gt; https://us8.api.mailchimp.com/3.0/campaigns
[body] =&gt; 
[timeout] =&gt; 10
[headers] =&gt; POST /3.0/campaigns HTTP/1.0
User-Agent: DrewM/MailChimp-API/3.0 (github.com/drewm/mailchimp-api)
Host: us8.api.mailchimp.com
Accept-Encoding: deflate, gzip
Accept: application/vnd.api+json
Content-Type: application/vnd.api+json
Authorization: apikey &lt;--api-key--&gt;
Content-Length: 0
)
</code></pre>

<p>I have checked the <a href="http://developer.mailchimp.com/documentation/mailchimp/reference/campaigns/#create-post_campaigns" rel="nofollow noreferrer">documentation</a>, searched through SO, but haven't found anything. If anyone has a working code that creates a simple campaign I can start working with, I would appreciate it. What am I missing?</p>