Application does not have permission error when tr

Question

I have facebook business account. I am seeing following error.

(#10) Application does not have permission for this action

When trying to add user to ad account using following code.

$attachment = array('access_token' => $accessToken,
'uid' => $fb_user_id,
'role' => '1001');

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,'https://graph.facebook.com/v2.8/act_'.$ad_account_id.'/users');
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $attachment);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$result = curl_exec($ch);

I have already Ads Management Basic Access, Ads Management API Standard Access and business_management access level.

I am doing RND on this from last few days but not getting any hint what can be the problem so can anyone give me suggestions what can be the exact problem?