Facebook : URL blocked This redirect failed because the redirect URI is not white-listed in the app's client OAuth settings - node.js

Question

Recently I have used Facebook Login option in my website. I have wrote all the APIs needed and tested them thoroughly in using "localhost" as domain. While configuring settings in my APP in Facebook developers account, I have setup all the necessary settings like giving Oauth redirect URL, adding domain name in basic settings and other things. Everything worked fine then. So, I have requested required app permissions like pages_manage_posts, pages_read_enagagment, pages_show_list and applied for them. Facebook approved them in the app review.
the Redirect URL ("https://execute.app/#/socialmedia/management/") that I used in Facebook is correctly put in the Facebook Oauth redirect URL path as shown in the pic below.
I have used server side APIs for Facebook login and graph APIs. I have used Oauth2 for Facebook login. You can see the code below
var OAuth2 = require('oauth').OAuth2;
var oauth2 = new OAuth2(CONSTANTS.FB_APP_Key,
CONSTANTS.FB_APP_Secret,
"", "https://www.facebook.com/dialog/oauth",
"https://graph.facebook.com/oauth/access_token",
null);
app.get('/api/document/facebook/auth', function (req, res) {
var redirect_uri = "https://execute.app/#/socialmedia/management/";
console.log("redirect_uri ", redirect_uri);
var params = { 'redirect_uri': redirect_uri, 'scope': 'email,public_profile,pages_manage_posts,pages_show_list,pages_read_engagement' };
var authUrl = oauth2.getAuthorizeUrl(params);
res.send({
"status": true,
"message": "login url generated successfully",
"url": authUrl
});
});
I will explain the problem in two scenarios below.
Scenario-1: When there is and existing active Facebook session in browser i.e, when some user is already logged into Facebook in facebook.com or developers.facebook.com and when we try to login into Facebook from our website, Oauth Authentication API gets called and returns Facebook login URL with status code 200 and the url gets opened in a new tab, its works fine, we don't need to enter Facebook login credentials again, we can just click on "**Continue as USER**" button and then we get the login code, with which we can get user access token. After getting token everything works as planned.
Scenario-2: But if no user is already logged into Facebook in browser and when I click on **login to Facebook** button, API call is made and it returns login URL, but the response status code sent by Oauth login API is 304. A new Facebook login tab is opened, but there is a warning displaying a message saying "URL blocked.
This redirect failed because the redirect URI is not white-listed in the app's client OAuth settings. Make sure that the client and web OAuth logins are on and add all your app domains as valid OAuth redirect URIs."
But you can see that I have added correct Redirect URL in Facebook already. It works in scenario-1 and does not work in another as I mentioned above.
Note: the Facebook login URL returned by Oauth Authentication API is same regardless the status code 200 or 304 . It goes as " https://www.facebook.com/dialog/oauth?redirect_uri=https%3A%2F%2Fexecute.app%2F%23%2Fsocialmedia%2Fmanagement%2F&scope=email%2Cpublic_profile%2Cpages_manage_posts%2Cpages_show_list%2Cpages_read_engagement&client_id=88XXXXXXX663"
Please help me in solving this issue ,thanks in advance

Answer 1

The OAuth RFC states for the redirect URI that:
The endpoint URI MUST NOT include a fragment component.
It might be a bug in Facebook that it works for some scenarios and does not work for others, but in fact it's best to avoid a URI with a fragment component. If Facebook's documentation states that you can use redirect URIs with fragments I would try to contact them ask why this doesn't work in some scenarios.