Error Using Facebook Login With Parse Server

you need to add the key facebookAppIds which contains an array of valid facebook app ids, this is mentioned here in the docs.

alternatively, add the FACEBOOK_APP_ID key as referenced [here] (https://github.com/ParsePlatform/parse-server/issues/82)

I don't know if you already had or tried this already but I was in a very similar situation as you and what fixed it for me was this:

In AppDelegate.swift, the ParseClientConfiguration must be initialized BEFORE the Parse Facebook Utils initialization in didFinishLaunchingWithOptions:

...// *** Initialize Parse. ***let config = ParseClientConfiguration(block: {    (ParseMutableClientConfiguration) -> Void in    ParseMutableClientConfiguration.applicationId = appKey;    ParseMutableClientConfiguration.clientKey = clientKey;    ParseMutableClientConfiguration.server = serverURL;});Parse.initializeWithConfiguration(config);// *NOTE: Putting the following line after after Parse.initializeWithConfiguration(config) fixed the issue// After this change, the user is no longer nil and does not print "Uh oh. The user cancelled the Facebook login.". Instead, it executes the `if let user = user` blockPFFacebookUtils.initializeFacebookWithApplicationLaunchOptions(launchOptions)...

Hope this helps at least somebody!

I had the same problem on a Parse Server running in Back4app.The solution was to add the Facebook App Id on the Back4app platform.