Unavailable action with Floating IPs API

I’m using the v2 API to assign Floating IPs to different droplets. It’s working great in Postman, however i’m having some issues getting it to work in PHP with CURL. I’m not sure quite where i’m going wrong, any pointers would be greatly appreciated!

https://developers.digitalocean.com/documentation/v2/#floating-ip-actions

Error:

 [id] => not_found
 [message] => The specified action type is not available

Code:

    /**
     * Change where a Floating IP Points
     *
     * @param string $floatingIp
     * @param int $dropletId
     * @return array
     */
    public function assignFloatingIp($floatingIp, $dropletId)
    {
        $data = array (
            'type' => 'assign',
            'droplet_id' => $dropletId
        );

        $response = $this->makeQuery('https://api.digitalocean.com/v2/floating_ips/'. $floatingIp .'/actions', 'POST', $data);

        if (!array_key_exists('action', $response)) {
            echo ucfirst($this->response['id']) . "<br>" . $this->response['message'];
        }

        return $response;
    }

    /**
    * Make query
    *
    * @param string $url
    * @param string $method
    * @param array $data
    * @return array
    */
    private function makeQuery($url, $method = 'GET', $data = null)
    {
        try {
            $headers = array('Authorization: Bearer '.$this->token);

            $curl = curl_init($url);
            curl_setopt($curl, CURLOPT_CONNECTTIMEOUT, 30);
            curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
            curl_setopt($curl, CURLOPT_CUSTOMREQUEST, $method);

            if ($data) {
                $data = json_encode($data);

                curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
                array_merge(
                    $headers,
                    array(
                        'Content-Type:application/json',
                        'Content-Length: ' . strlen($data)
                    )
                );
            }

            curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);

            //Data are stored in $data
            $response = json_decode(curl_exec($curl), true);
            curl_close($curl);

            return $response;
        } catch (Exception $e) {
            return $e->getMessage();
        }
    }