I wanted to add following meta tag:
<meta name="google-site-verification" content="XXXXXXXXXXXXXXXXXXXXXXXXXXX" />
For that I used Admin > Config > Search and Metadata > Custom Meta tags Setting
And created meta tag there.
But the meta tag is not visible in page source code in browser.
Version: 7.35 The meta tag i added appears in list of meta tags here.
Here is a way for you to find an issue.
Below you will find a screen of function that adds tags to header.
According to conditions you have possibly next issues:
$meta_tags is null. It means that this query return nothing
$result = db_query("SELECT * FROM {custom_meta}");
you have 'admin' as an argument.
Please debug those 2 variables ($meta_tags and arg(0) and provide us feedback.
dpm($meta_tags);
dpm(arg(0));
I believe you will figure out during debug the issue.