<?php

require 'vendor/autoload.php';

$headers = array(
    'Accept' => 'application/json',
    'Authorization' => 'Bearer {access-token}',
    // The x-fax-clientid header is required only when using the OAuth2 token scheme
    'x-fax-clientid' => '{client ID}',
);

$client = new GuzzleHttp\Client();

// Define array of request body.
$request_body = ...;  // See request body example

try {
    $response = $client->request('POST','https://restapi.fax.plus/v3/accounts/{user_id}/outbox', array(
        'headers' => $headers,
        'json' => $request_body,
        )
    );
    print_r($response->getBody()->getContents());
 }
 catch (GuzzleHttp\Exception\BadResponseException $e) {
    // handle exception or api errors.
    print_r($e->getMessage());
 }

 // ...