petition not found error

[Widi Oremo]

//I have the following function
//I keep getting this response {"result":"failure","messages":["petition not found"]}
//I have checked and checked my code again but I cant see what's wrong.
//Kindly assist.


public function get_auth_key(){

    

  $api_key = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';

  $secret_token = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';

  $petition_id = xxxxxxx;

  $host = 'https://api.change.org';

  $endpoint = '/v1/petitions/$petition_id/auth_keys';

  $request_url = $host . $endpoint;

  $params = array();

  $params['api_key'] = $api_key;

  $params['source_description'] = 'Petition website'; // Something human readable.

  $params['source'] = base_url(). '/change_dot_org/get_auth_key'; // Eventually included in every signature submitted with the auth key obtained with this request.

  $params['requester_email'] = 'wezxxxxxx...@gmail.com'; // The email associated with your API key and Change.org account.

  $params['timestamp'] = gmdate("Y-m-d\TH:i:s\Z"); // ISO-8601-formtted timestamp at UTC

  $params['endpoint'] = $endpoint;

  $params['callback_endpoint'] = base_url(). '/change_dot_org/get_auth_key';

  

  // Build request signature and add it as a parameter

  $query_string_with_secret_and_auth_key = http_build_query($params) . $secret_token;

  $params['rsig'] = hash('sha256', $query_string_with_secret_and_auth_key);

  // Final request body

  $query = http_build_query($params);

  // Make the request

  

  

  /////////////////////////////////////

  

   $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, $request_url);

        curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 5);

        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

        curl_setopt($ch, CURLOPT_POSTFIELDS, $query);

        $response = curl_exec($ch);

        if (curl_errno($ch)) {

            echo curl_error($ch);

            echo "\n<br />";

            $response = '';

        } else {

            curl_close($ch);

        }

        if (!is_string($response) || !strlen($response)) {

            echo "Failed to get contents.";

            $response = '';

        }

        echo $response;

       

        die();

  

  

  

  ////////////////////////////////////

  

}