Always get "Error validating verification code." when requesting access_token <p>Well, I have done all my best to try to solve this problem, but, still, it's too annoying.</p> <p><p>I decided to use OAuth with server-side authentication. So, I have followed Facebook documentation, and I have done the following step.</p> <ol> <li>Create a link which redirect people to log in Facebook by <code>https://www.facebook.com/dialog/oauth?client_id={APP_ID}&amp;redirect_uri=http://abc.com/nextStep.php</code></li> <li>In nextStep.php, redirect people to <code>https://graph.facebook.com/oauth/access_token?code={CODE GENERATED BY FACEBOOK}&amp;client_id={APP_ID}&amp;redirect_uri=http://abc.com/thirdStep.php&amp;client_secret={APP_SECRET}</code></li> </ol> <p>The problem exists when proceeding to step 2. The page shows that:</p> <pre><code>{ "error": { "message": "Error validating verification code.", "type": "OAuthException", "code": 100 } } </code></pre> <p>I have googled for lots of time. Some people suggests to add a trailing slash in the redirect_uri, but it doesn't work. What should I do? And how can I get the user information after getting the access_token? Thanks for your help.</p>