1. What is the value of the redirect URI that you've set in your Instagram application? It should be in the format
www.YOURDOMAIN.com/index.php.
2. What is the specific URL of the page that you're trying to log in from?
3. If you have a valid SSL certificate installed on your site, you should use the https in the redirect_uri link. In JFBConnect, make sure you enable the "Use SSL For Authentication" setting in the Instagram configuration section.
-Melissa