Может так?
<?php
$curl = curl_init();
curl_setopt_array($curl, array(
CURLOPT_URL => "https://api.telegram.org/bot598******:AAFx8OAg8dj184XBTldynqezf64trbOQ/sendMessage",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 0,
CURLOPT_FOLLOWLOCATION => true,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS =>"{\"chat_id\":\"2367*****\",\"text\":\"test message here\"}",
CURLOPT_HTTPHEADER => array(
"Content-Type: application/json"
),
));
$response = curl_exec($curl);
curl_close($curl);
echo $response;