Sample POST to Slack API method chat.postMessage

gistfile1.php

$payload = array(
    'token' => 'xxxx-xxxxxxxxx-xxxx',
    'channel => 'C1234567890',
	 	'attachments' => array(array(
	 		'text' => "This is my post body",
	 		'fallback' => "This is the fallback"
	)));
	
$data_str = json_encode($payload);
	
curl_setopt($ch, CURLOPT_URL, 'https://slack.com/api/chat.postMessage');                                                                                                                              
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");                                                                     
curl_setopt($ch, CURLOPT_POSTFIELDS, $data_str);                                                                  
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);                                                                      
curl_setopt($ch, CURLOPT_HTTPHEADER, array(                                                                          
    'Content-Type: application/json',                                                                                
    'Content-Length: ' . strlen($data_str))                                                                       
);

$res = curl_exec($ch);                                                                                                                   

print_r($res);

curl_close($ch);