How can I determine the cause of a failed webservice connection in PHP? [duplicate]

I have a PHP code that allows me to connect to a webservice and retrieve the response.

If I run this code locally on my computer without any particular configuration, it works. But as soon as I run it on my web server, I get this error:

The PHP version currently running is :

PHP 7.1.5 (cli) (built: May 9 2017 19:48:36) ( NTS MSVC14 (Visual C++ 2015) x64 ) Copyright (c) 1997-2017 The PHP Group Zend Engine v3.1.0, Copyright (c) 1998-2017 Zend Technologies 

SOAP Fault: WSDL, SOAP-ERROR: Parsing WSDL: Couldn't load from 'https://ws.chronopost.fr/shipping-cxf/ShippingServiceWS?wsdl' : failed to load external entity "https://ws.chronopost.fr/shipping-cxf/ShippingServiceWS?wsdl"

• I had an old version of PHP in 5.3.9, I modified to run one in 7.1.5, same error.
• I can connect to the webservice from Postman with my credentials.
• I tried to disable SSL verification in my code, same error.
• I can open the url from a server browser.
• The firewall doesn’t block anything in particular.
• I’ve managed to connect without error using nuSOAP, but I can’t retrieve the response returned by the webservice.

I’ve already done what is indicated in this answer: SOAP PHP fault parsing WSDL: failed to load external entity? and the result is the same. That’s why I’m asking this question.

How can I determine the cause of the problem?
Thanks for your help,

My code:

<?php

// Specify the full path to the PHP executable
$chemin_php = "C:\php\php7.1.5\php.exe";

// Execute the command to obtain the PHP version
$version_php = shell_exec("$chemin_php -v");

// Display PHP version
echo "The PHP version currently running is : <br>";
echo $version_php;

// URL du service WSDL
$wsdlUrl = 'https://ws.chronopost.fr/shipping-cxf/ShippingServiceWS?wsdl';

$requestUrl = 'https://ws.chronopost.fr/shipping-cxf/ShippingServiceWS';

  // the soap operation which is called
$action = 'euExpressRateBook_providerServices_ShipmentHandlingServices_Binder_createShipmentRequest';
  // the xml input of the service
  $xmlrequest = '<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:cxf="http://cxf.shipping.soap.chronopost.fr/">
  <soapenv:Header/>
  <soapenv:Body>
//rest of the code
</soapenv:Body>
</soapenv:Envelope>';

try {
    $options = array();
    $options['wrapper'] = array(
        
        'soap_version' => 'SOAP_1_1',
        'encoding' => 'UTF-8',
        'user_agent' => 'PHPSoapClient',
        
        // The exceptions option is a boolean value defining whether soap errors throw exceptions of type SoapFault.
        'exceptions' => true,
        
        // The trace option enables tracing of request so faults can be backtraced.
        'trace' => true
    );
    
    
    $context = stream_context_create($options);
    // create the soapclient and invoke __doRequest method
    //WSDL URL is called on init
    $client = new SoapClient($wsdlUrl, $options);
    //Here we call REQUEST URL
    $output = $client->__doRequest($xmlrequest, $requestUrl, $action, 1);

    // Affichez la réponse SOAP
    echo "Réponse SOAP :<br>";
    echo htmlentities($output);
}
catch (SoapFault $fault) {
    var_dump($fault);
    echo "<h2>SOAP Fault!</h2><p>";
    echo "FaultCode: {$fault->faultcode} <br/>";
    echo "FaultString: {$fault->faultstring} <br/>";
    echo("</p/>");
}