Using cURL to return API XML response - php

Question

Forgive me if this is simple. My research has brought me to a halt at the moment. I am trying to use cURL to get the response of an API in XML.
This is the URL of the API: https://api.weather.gov/alerts/active/region/land
By default it returns in JSON. Which I know, I should just use the JSON response but, there is a reason I need it in XML as it will seamlessly integrate into my current code until I can rewrite it for JSON.
This is the documentation for the API. Under the API Reference tab is states I just need to change the request header to application/cap+xml. But I am not getting anything back. Just a blank white page.
https://alerts-v2.weather.gov/documentation
Here is my current code I am using to call the API but I get no response or anything. What am I missing?
<?php
$headers[] = 'Connection: Keep-Alive';
$headers[] = 'Content-Type: application/cap+xml;charset=utf-8';
$headers[] = 'Accept: application/cap+xml';
$userAgent = 'php';
$url = 'https://api.weather.gov/alerts/active/region/land';
$cURL = curl_init();
curl_setopt($cURL, CURLOPT_URL, $url);
curl_setopt($cURL, CURLOPT_HTTPHEADER, $headers);
curl_setopt($cURL, CURLOPT_USERAGENT, $userAgent);
curl_setopt($cURL, CURLOPT_RETURNTRANSFER, true);
curl_setopt($cURL, CURLOPT_HTTPGET, true);
$result = curl_exec($cURL);
curl_close($cURL);
?>

Answer 1

I've just tried your code and it works fine with atom:
$headers[] = 'Accept: application/atom+xml';
"application/cap+xml" is not available for the URLs, like you mentioned in a question though.
Per the doc https://alerts-v2.weather.gov/documentation the formats are following:
/alerts/active/region/{region} => JSON-LD (default), ATOM
/alerts/{alertId} => JSON-LD (default), CAP