require_once('/path/to/GlobalCheckout/vendor/autoload.php');

<?php
require_once(__DIR__ . '/vendor/autoload.php');

// Configure OAuth2 access token for authorization: OAuth2
$config = UPS\GlobalCheckout\Configuration::getDefaultConfiguration()->setAccessToken('YOUR_ACCESS_TOKEN');

$apiInstance = new UPS\GlobalCheckout\Request\GlobalCheckoutApi(
    // If you want use custom http client, pass your client which implements `GuzzleHttp\ClientInterface`.
    // This is optional, `GuzzleHttp\Client` will be used as default.
    new GuzzleHttp\Client(),
    $config
);
$trans_id = new \UPS\GlobalCheckout\GlobalCheckout\null(); //  | An identifier unique to the request.
$transaction_src = new \UPS\GlobalCheckout\GlobalCheckout\null(); //  | Identifies the client/source application that is calling.
$accept = new \UPS\GlobalCheckout\GlobalCheckout\null(); //  | The Accept request HTTP header indicates which content types, expressed as MIME types, the client is able to understand.
$content_type = new \UPS\GlobalCheckout\GlobalCheckout\null(); //  | The Content-Type header provides the client with the actual content/media type of the returned content.
$body = new \UPS\GlobalCheckout\GlobalCheckout\BSISV1QuoteRequest(); // \UPS\GlobalCheckout\GlobalCheckout\BSISV1QuoteRequest | 
$registration_id = new \UPS\GlobalCheckout\GlobalCheckout\null(); //  | The Customer Registration Identifier used to validate the shipper account.  If not passed then it will be obtained with the OAuth token's UUID.

try {
    $result = $apiInstance->createGuaranteedQuote($trans_id, $transaction_src, $accept, $content_type, $body, $registration_id);
    print_r($result);
} catch (Exception $e) {
    echo 'Exception when calling GlobalCheckoutApi->createGuaranteedQuote: ', $e->getMessage(), PHP_EOL;
}
?>