webhook.php

<?php
/**
 * Processes the message requested
 *
 * @param $update
 */
function processMessage($update)

	switch ($update["queryResult"]["action"]) {

        case "test.hook";
            sendMessage(array(
                "fulfillmentMessages" => array([
                    "platform" => "ACTIONS_ON_GOOGLE",
                    "simpleResponses" => array("simpleResponses" => [array(
                        "textToSpeech" => "Api request has been solved",
                        "displayText" => "Api request has been solved"
                    )])]
                )));
    }
}

/**
 * Encodes the parameters given, and echoes them
 *
 * @param $parameters
 */
function sendMessage($parameters)
{
    echo json_encode($parameters);
}

// Things starts here
$update_response = file_get_contents("php://input");
$update = json_decode($update_response, true);

// Open debug file, to write the request to
$myFile = fopen("debug.txt", "w") or die("Unable to open file!");
ob_start();
var_dump($update_response);
$result = ob_get_clean();
fwrite($myFile, $result);
fclose($myFile);

if (isset($update["queryResult"]["action"])) {
    processMessage($update);
}