Cannot make a cURL request through a proxy in PHP

Question

I am trying to make a cURL request through a proxy in PHP but the page never loads. If I use the same proxy via shell commands it works perfectly and I get the response. Here's the code on PHP:

 $url = "https://example.com"
 $myvars = "key1=value1&key2=value2;

 $ch = curl_init( $url );

 curl_setopt($ch, CURLOPT_PROXY, '172.93.148.247');
 curl_setopt($ch, CURLOPT_PROXYPORT, '3128');

 curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Content-Type: application/x-www-form-urlencoded; charset=utf-8' 
));
 curl_setopt( $ch, CURLOPT_POST, 1);
 curl_setopt( $ch, CURLOPT_POSTFIELDS, $myvars);
 curl_setopt( $ch, CURLOPT_FOLLOWLOCATION, 1);
 curl_setopt($ch, CURLOPT_VERBOSE, true);
 curl_setopt( $ch, CURLOPT_HEADER, 0);
 curl_setopt( $ch, CURLOPT_RETURNTRANSFER, 1);

Shell command (works):

curl --proxy 172.93.148.247:3128 -v -X POST 'https://example.com' -H 'Content-Type: application/x-www-form-urlencoded; charset=utf-8' -H 'Cookie:' -d "key1=value1&key2=value2"