How can I add localhost:3000 to Facebook App for development

On the Facebook App page, click "edit App" then click "Advanced" in the left-hand navigation. Then for "Valid OAuth redirect URIs" add http://localhost:3000... or whatever you want the accepted redirect to be.

You can create a test app that's connected to your main app. On the Dashboard or Settings page for your main app. scroll down and you'll see "Test Apps" in the menu that runs down the left side of the page. The test app will inherit settings from the main app, but it will permanently be in development mode, and it will have its own ID.

More info on test apps here:https://developers.facebook.com/docs/apps/test-apps/

The protocol for setting up an app to work on localhost has changed. After you get your test app set up, this explains the steps for setting it up to work on localhost:

https://stackoverflow.com/a/24253054/2803458

Your error is saying

localhost URL is not allowed in the application

I know, FB does not give a s**t about explaining, what do to in those moments, however, as far as I am concerned, I have found workaround.

Basically, you need to "whitelist" locahost url in your app

Here is what you are going to do

1. Go to the app edit/summary page
2. In the fourth field App Domains, you should already have roomidex.com, so add another address localhost
3. The urls mentioned above are only valid, if each one of them is put into tabs, where you set, how you app integrates with Facebook (website with facebook login, App on facebook, Mobile web, …)
4. I do this: I put my working URL, in your case roomidex.com into Website with facebook login, and my test, localhost URL, either into App on facebook or Page tab