appid custom field wordpress

Hello everyone, I created an application on facebook and would like to integrate it to a post on my wordpress. This case, the Canvas Application URL facebook would be done in wordpress.
So I made the call code from facebook in my single.php file
adding code at the top of the file single.php
<? php
/ ** Your unique ID from Facebook applications * /
$ appid = ‘XXXXXX’;
/ ** Your Facebook applications secret * /
$ appsecret = ‘XXXX’;?>

My doubt is being the following:
I want to call the appid and appsecret through a custom field, but I can not.
I tried to add the code below into the field ‘XXX’ but to no avail
  <? php
global $ wp_query;
$ postid = $ wp_query-> post-> ID;
echo get_post_meta ($ postid, ‘CUSTOM FIELD’, true);
wp_reset_query ();
?>
this code above is to run the custom field outside the loop, I added it in the field where I add the application number ($ appid), but not forward. The Custom field not just run inside the php code of facebook.

Anyone know the correct way to call the number of the application through a custom field?