1. I think the redirect_uri value is incorrect in your request. It doesn't match the URL you gave at the time of your Facebook app registration. To get the correct value of redirect_uri, login to https://developers.facebook.com/, navigate to your app by clicking My Apps link at the top. Click Settings on the left. You will find redirect_uri mentioned under Site URL field (see screenshot below).
2. You should always URL encode redirect_uri value. For example, in the above screenshot, my redirect_uri is https://foo.bar. So my authorization request should look like this: