php - Cant get app access token

Im desperately trying to get the app access token and failing miserably. Perhaps someone code help

The first way i am trying to get is below :

try {
    $access_t = $facebook->api(
        '/oauth/access_token', 'get', array(
            'client_id'     => $app_id,  
            'client_secret' => $app_secret, 
            'redirect_uri'  => $canvas_page_url
        )
    );
} catch (FacebookApiException $e) {
    echo $e;
} 
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I get the error "AuthException: An unknown error has occurred." I confess im not sure what url i should be using for $canvas_page_url So i have used my apps.facebook.com/appname url

Any ideas?

The second way i am trying is :

$token_url = 'https://graph.facebook.com/oauth/access_token?'
    . 'client_id=' . $app_id
    . '&client_secret=' . $app_secret
    . '&grant_type=client_credentials';
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And although this does return a access token i am reading that in fact its wron g... Not long enough?

result = 248119721897385|LvWcoYbWu2lQlkEN0HDOeIupSqs
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Any ideas on this would be really appreciated as its been doing my head in for some time now.