open website only if refer is facebook

i want to allow users to see website only if refer is from facebook
facebook page or timeline or like that...
if refer is direct or from google i want to block him

i have these code where is my mistake?

<?php

$allowed_domains = array('www.facebook.com/','https://www.facebook.com/');

$REFERRER = $_SERVER['HTTP_REFERER'];

if ($REFERRER == '') {
    // works
}

$domain = substr($REFERRER, strpos($REFERRER, '://')+3);
$domain = substr($domain, 0, strpos($domain, '/'));

if (!in_array($domain, $allowed_domains)) {
    exit(header('Location: error.php'));
}

?>

Code (markup):

 

Give this a try, I think the problem is the / you left on one of the domains:

NOTE: I disabled the redirect for my testing.

<?php

$allowed_domains = array('www.facebook.com/','https://www.facebook.com/','www.facebook.com');

//$REFERRER = $_SERVER['HTTP_REFERER'];

$REFERRER = "https://www.facebook.com/";


if ($REFERRER == '') {
  echo "No";
}

$domain = substr($REFERRER, strpos($REFERRER, '://')+3);

$domain = substr($domain, 0, strpos($domain, '/'));

if (!in_array($domain, $allowed_domains)) {

  echo "No";

  //exit(header('Location: error.php'));
}
else {

  echo "I am allowed";

}

?>

Code (markup):

 

Just have to add that to the list:

$allowed_domains = array('www.facebook.com/','https://www.facebook.com/','www.facebook.com','m.facebook.com');