cURL makes page load forever, then gateway timed out - php

Question

I'm working with a third party API, and it returns 400 HTTP STATUS when you make a mistake.
When using POSTMAN, the 400 HTTP error page shows as expected, but when using PHP's cURL, the page just loads for about a minute, then it gives me a "504 - Gateway timeout", and I need to close the browser to be able to access the page again.
When the cURL request is valid (the API returns a 200 OK) it works normally.
My question is, why is cURL giving the 504 error instead of 400?
And why is it ignoring CURLOPT_CONNECTTIMEOUT and CURLOPT_TIMEOUT?
Below is my cURL code (both $token, $payload and $config variables are declared and valid):
$ch = curl_init("https://api.mercadolibre.com/items?access_token=$token");
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 10);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
"User-Agent: Alcavie/" . $config['version'],
"Accept: application/json",
"Content-Type: application/json",
//"Accept-Encoding: gzip, deflate, br",
//"Connection: keep-alive"
));
$error = false;
try{
$result = curl_exec($ch);
$resultJson = json_decode($result);
}catch(\Exception $e){
var_dump($e);
$error = true;
exit;
}
curl_close($ch);

Answer 1

The API probably sends HTTP302 in between and if so, you'd either need two requests ortell cURL to follow the redirect with curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);HTTP504 means that the client didn't react in a timely manner upon the previous HTTP header;there may be other causes for HTTP504, but it is one of the most common. Postman is insufficient to test this properly (I don't use it at all); better use a web-browser, hit F12 and tick the "preserve logs" checkbox... then you can clearly see which HTTP headers are being sent in succession.
Also useful to debug this would be: curl_setopt($ch, CURLOPT_HEADER, true);