I'm trying to make a login with Facebook available in my script. I've done everything, but when I attempt to login with a Facebook account I get this error from Facebook:
Error
App Not Setup: The developers of this app have not set up this app properly for Facebook Login.
Here's error screenshot:

Any ideas?
This error is caused by a configuration issue in your Facebook Developer Application. This means your Facebook app is not live.
You can access the Developer Settings panel by going to the Apps panel or developers.facebook.com/docs, hovering over your profile image in the upper right corner, and selecting Developer Settings from the dropdown menu.
Ensure that you have enabled App auth within the Facebook development console, check that you have all the essential setup steps, and provided a current and valid privacy policy. Once your health checks are in place, your app should be valid to authenticate with your firebase app.
the problem was you have to set
Do you want to make this app and all its live features available to the general public?
set status and review to ON and problem solved
enjoy coding
With respect to the all the other answers, here's the screenshot to help someone.

The circle next to your app name is not fully green. When you hover mouse on it, you'll see a popup saying, "Not available to all users because your app is not live."
So next, you've to make it publicly available.


Since the UI of the facebook has changed recently, here's the latest update for setting the sandbox mode ON/OFF :
Go to https://developers.facebook.com/
Click on the Apps menu on the top bar.
Select the respective app from the drop down.
Go to 'Status & Review' from the table in the left side of the page.
Do you want to make this app and all its live features available to the general public? - Select switch to set YES/NO value.
Update: The YES/NO button will be disabled until and unless you provide your contact email.
Go to "Settings" in the left menu.
Update your Contact Email.
Hit the "Save" button at the bottom of the page.
Update: 'Status & Review' is replaced by 'App Review' now
If the app is still in private mode (Status and Review set to NO), then only Facebook users with role in the app can login.
That unless you set it to public (Status and Review set to YES).
To add more users to be able to login to a private app:
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