504 Gateway time out php - php

Question

i'm running script(svc/rest services) that request a server which response me a XML string.. this request is going through an intermediate server.
My aim is to fetch the details of guests o.e. rooms which will be response..
but after certain number of request i am getting 504 gateway out and only about 40 rooms are able to retreived
1: file...source hots
$ROOMS = ["301","302","304","305","306","307","308","309","310",
"311","312","314","315","316","317","318","319","320",
"401","402","403","404","405","406","407","408","409",
"410","411","412","414","415","416","802","802","802",
"802","802","802","802","802","802","802","802","802",
"802","802","802","802","802","802","802","802","802",
"802","802","802","802","802","802","802","802"
];
// all rooms more than 75
for ($x = 0; $x < count($ROOMS); $x++){
$end_point = "https://www.innkeyapp.com/SerRest.svc/GetOccupiedRoomData";
$sharedkey = "2diSq8bjZ4N3ZR4XB5KXXXXXXXXXXXXXXXXXXXXXXX";
$url = 'https://eastern-services.com/innkeyPMS_room_ststus.php';
$room_no = $ROOMS[$x];
$postdata = http_build_query([
'end_point' => $end_point,
'room_no' => $room_no,
'sharedkey' => $sharedkey
]);
$opts = [
'http' => [
'method' => 'POST',
'content' => $postdata
]
];
$context = stream_context_create($opts);
$result = file_get_contents($url, false, $context);
$arrayData = json_decode($result,true);
if (empty($arrayData)) {
// Redirect('failure.php?msg=Error in service');
echo "Error in Service";
exit();
}
print_r($arrayData);
echo $room_no."Added";
}
2: file.... innkeyPMS_room_ststus.php i.e. intermediate host.
$room_no = $post_var['room_no'];
$end_point = $post_var['end_point'];
$sharedkey = $post_var['sharedkey'];
$registerno = '';
$prprtxt = '';
$validunit = '';
// echo $post_var;
function curl_get_file_contents($URL)
{
return file_get_contents($URL);
}
$xmlString = curl_get_file_contents(
$end_point.'sharedkey='.$sharedkey.'=&roomno='.$room_no
);
$xml = simplexml_load_string($xmlString);
header("Content-Type: application/json");
echo json_encode($xml);
why this connection is getting lost or why its showing 504 gateway time out?