Invalid access token facebook error for facebook graph api - facebook

Question

I am using below curl code which is based on #unificationengine API to access facebook graph api and post message on facebook:
$post_msg = json_encode(
array(
'message' =>
array(
'receivers' =>
array(
array(
'name' => 'Me',
'address' => 'https://graph.facebook.com/v2.5/7/feed?access_token='.$request->access_token,
'Connector' => 'facebook'
),
),
'sender' =>
array('address' => 'sender address'),
'subject' => 'Hello',
'parts' =>
array(
array(
'id' => '1',
'contentType' => 'text/plain',
'data' => 'Hi welcome to UE',
'size' => 100,
'sort' => 0
),
),
),
)
);
$ch = curl_init('https://apiv2.unificationengine.com/v2/message/send');
curl_setopt($ch, CURLOPT_USERPWD, "ab33333222b-acb5-49a6-a766-80d991daff41:43433232-33cb-49f0-3333-3fe6c46acb5f");
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch, CURLOPT_VERBOSE, true);
curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
curl_setopt($ch, CURLOPT_POSTFIELDS, $post_msg);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
// execute!
$response = curl_exec($ch);
// close the connection, release resources used
curl_close($ch);
// do anything you want with your response
var_dump($response);
return ['label' =>$response];
I am getting invalid access token error with code 498. I referred various posts on this topic but couldn't figure out that what is missing.
How to check validity of facebook access token.
Referenced these questions:
SO question 1
SO question 2

Answer 1

The facebook access tokens have a lifetime of about two hours. For longer lived web apps, especially server side, need to generate long lived tokens. Long lived tokens generally lasts about 60 days.
UE has a capability to refresh facebook tokens. After adding connection using "apiv2.unificationengine.com/v2/connection/add"; api call, then you should call "apiv2.unificationengine.com/v2/connection/refresh"; api to make the short lived token to long lived.