Sometimes, especially if building a custom theme... or if you've started with a flat HTML/CSS/JS page and turned it into a Drupal theme.... the MetaTag data doesn't display in the <head> area. This might be because I've used a node as the home page, or maybe something is causing a problem elsewhere, but the problem is the same. After a little research I found the solution was to add the following to your template.php file.
function THEMENAME_preprocess_html(&$vars) {
if(isset($vars['page']['content']['metatags'])){
render($vars['page']['content']['metatags']);
}
}
Replace THEMENAME with the name of your theme...
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