mPDF failed to open stream: operation failed - mpdf

Question

mPDF stopping working for me, pdfs generated from php are now blank, when I turn on debug I get the following error message.
Error detected. PDF file generation aborted: file_get_contents(https://www.myurl.com/pdf.php): failed to open stream: operation failed
When I go directly to the php page it appears fine.
Here is the code I'm using, I changed permissions to 777 on the file and the folder and it still doesn't work yet if I change the url to an external one it works perfectly. So I'm guessing something on my server is blocking it.
require __DIR__ . '/vendor/autoload.php';
$invoice_id = $_GET['invoice_id'];
$url="https://www.myurl.com/pdf.php";
if (ini_get('allow_url_fopen')) {
$html = file_get_contents($url);
} else {
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt ( $ch , CURLOPT_RETURNTRANSFER , 1 );
$html = curl_exec($ch);
curl_close($ch);
}
try
{
$mpdf = new \Mpdf\Mpdf();
$mpdf->debug = true;
$mpdf->SetDisplayMode('fullwidth');
$mpdf->CSSselectMedia='mpdf'; // assuming you used this in the document header
$mpdf->setBasePath($url);
$mpdf->WriteHTML($html);
$mpdf->Output('invoice'.$invoice_id.'.pdf','D');
} catch (\Mpdf\MpdfException $e) { // Note: safer fully qualified exception
echo $e->getMessage();
}