Something like this should do it, there are a lot of post on using cUrl with PHP
How to POST JSON Data With PHP cURL? , Set bearer token with cURL
<?php
$curl_handle=curl_init();
curl_setopt($curl_handle,CURLOPT_URL,'https://open.faceit.com/chat/v1/rooms/hub-4d2be024-1573-4312-9c56-425003027f08-general/messages');
curl_setopt($curl_handle,CURLOPT_CONNECTTIMEOUT,2);
$authorization = "Authorization: Bearer ".$token;
curl_setopt($curl_handle, CURLOPT_HTTPHEADER, array('Content-Type: application/json' , $authorization ));
# Return response instead of printing.
curl_setopt( $curl_handle, CURLOPT_RETURNTRANSFER, true );
$post = json_encode(["body"=>"test"]);
curl_setopt($curl_handle, CURLOPT_POSTFIELDS, $post);
$buffer = curl_exec($curl_handle);
curl_close($curl_handle);
if (empty($buffer)){
print "Nothing returned from url.<p>";
}
else{
print $buffer;
}
?>