ios facebook sdk 4.0 login error code 304

I had a similar problem.

After initialising FBSDKLoginManager I added a line to flush out the data and the (Facebook)Token:

FBSDKLoginManager *loginmanager= [[FBSDKLoginManager alloc]init];    
[loginmanager logOut];

Hope this helps.

Thus, exactly as the OP asks, "am I missing something"?

Yes, the following standard example code which is seen everywhere, is simply wrong:

-(IBAction)facebookLoginClick:(id)sender
{
FBSDKLoginManager *login = [[FBSDKLoginManager alloc] init];
---- ONE MAGIC LINE OF CODE IS MISSING HERE ----
[login logInWithReadPermissions:@[@"email"]
   handler:^(FBSDKLoginManagerLoginResult *result, NSError *error)
    {
    if (error) {...}
    else if (result.isCancelled) {...}
    else { // (NB for multiple permissions, check every one)
       if ([result.grantedPermissions containsObject:@"email"])
          { NSLog(@"%@",result.token); }
       }
}];
}

you must do this:

-(IBAction)facebookLoginClick:(id)sender
{
FBSDKLoginManager *login = [[FBSDKLoginManager alloc] init];
[login logOut];   //ESSENTIAL LINE OF CODE
[login logInWithReadPermissions:@[@"email"]
   handler:^(FBSDKLoginManagerLoginResult *result, NSError *error)
    {
    if (error) {...}
    else if (result.isCancelled) {...}
    else { // (NB for multiple permissions, check every one)
       if ([result.grantedPermissions containsObject:@"email"])
          { NSLog(@"%@",result.token); }
       }
}];
}

Otherwise, very simply, the app will not work if the user happens to change FB accounts on the device. (Unless they happen to for some reason re-install the app!)

Once again - the popular sample code above simply does not work (the app goes in to an endless loop) if a user happens to change FB accounts. The logOut call must be made.

I had this, it occurred when changing the FB app details in Xcode while an iOS app was running. You need to delete the app from the device and then republish with the new FB app setup. Just recompiling is not enough to clear the old FB settings

This happened to me when I changed the Facebook AppID (in the Info.plist file) switching form a test Facebook app to a production Facebook app. If your app sends the Facebook token to a server that generate a JWT for for instance, Facebook SDK still persists the fbToken (FBSDKAccessToken.currentAccessToken()) persisted unless it's told to remove it. That may also happen in production when a user logs out of the app, a log out API request will log the user out and reset your JWT. But even before sending the log out API request, the client will need to tell the FBSDKLoginManager instance to log out.

if let currentAccessToken = FBSDKAccessToken.currentAccessToken() where currentAccessToken.appID != FBSDKSettings.appID()
    {
        loginManager.logOut()
    }

You can use the following code to solve your problem :

[FBSDKAccessToken refreshCurrentAccessToken:^(FBSDKGraphRequestConnection *connection, id result, NSError *error){}

Swift 3.0

func loginWithFacebook
{
        let loginManager = FBSDKLoginManager()
        if let currentAccessToken = FBSDKAccessToken.current(), currentAccessToken.appID != FBSDKSettings.appID()
        {
            loginManager.logOut()
        }

        loginManager.logIn(withReadPermissions: ["public_profile","email"], from: self, handler: { (result, error) in
            if error != nil {
                print("error\(String(describing: error))")
            }
            else if (result?.isCancelled)! {
            }
            else {
                print(FBSDKAccessToken.current())
            }
        })
}

According to the docs, 304 FBSDKLoginUserMismatchErrorCode "Indicates a failure to request new permissions because the user has changed".

Make sense in the scenario @Adrian999 mentioned.

Actually, the reason is very simple, you can try following step to reappear this error code easily.

The "Facebook login fail" may have two reasons:

1. you get the user info from facebook fail.
2. you get the user info from facebook success,but upload to your own server fail.

The code in FBSDKLoginManager.m is:

- (void)validateReauthentication:(FBSDKAccessToken *)currentToken withResult:(FBSDKLoginManagerLoginResult *)loginResult
{
  FBSDKGraphRequest *requestMe = [[FBSDKGraphRequest alloc] initWithGraphPath:@"me"
                                                                   parameters:nil
                                                                  tokenString:loginResult.token.tokenString
                                                                   HTTPMethod:nil
                                                                        flags:FBSDKGraphRequestFlagDoNotInvalidateTokenOnError | FBSDKGraphRequestFlagDisableErrorRecovery];
  [requestMe startWithCompletionHandler:^(FBSDKGraphRequestConnection *connection, id result, NSError *error) {
NSString *actualID = result[@"id"];
  if ([currentToken.userID isEqualToString:actualID]) {
    [FBSDKAccessToken setCurrentAccessToken:loginResult.token];
    [self invokeHandler:loginResult error:nil];
  } else {
    NSMutableDictionary *userInfo = [NSMutableDictionary dictionary];
    [FBSDKInternalUtility dictionary:userInfo setObject:error forKey:NSUnderlyingErrorKey];
    NSError *resultError = [NSError errorWithDomain:FBSDKLoginErrorDomain
                                             code:FBSDKLoginUserMismatchErrorCode
                                         userInfo:userInfo];
   [self invokeHandler:nil error:resultError];
  }
}];
}

when currentToken.userID is not equal actualID, the FBSDKLoginUserMismatchErrorCode will throw.

Now, this issue will reappear when user A login facebook fail,but you do not have [FacebookSDKManager logOut] after the fail, the app will cache the accessToken for the user A , and then user A change facebook account to user B, when user B login facebook again,it will reappear this issue.

I was also stuck on this issue for a while. then i created object for FBSDKLoginManager in .h file and in viewDidLoad of .m file , initialize it and set logout property.

 _fbLogin= [[FBSDKLoginManager alloc]init];    
 [_fbLogin logOut];

This helped me and hope helps you as well. All the best.

Thanks

Swift 4.0 and FBSDKCoreKit 4.33

let loginManager = LoginManager()
if let currentAccessToken = AccessToken.current, currentAccessToken.appId != SDKSettings.appId
{
    loginManager.logOut()
}

swift 4.0, 4.2, 5.0

FBSDKLoginManager().logOut()

Single Sign On

I've also found that this issue happens if you have an app that does not require single sign on (i.e. an app which multiple users will create content and share from one device).

You can change single sign on in your app settings https://developers.facebook.com/apps/your-app-id/settings/.

For me in Objective-C following worked

FBSDKLoginManager *login = [[FBSDKLoginManager alloc] init];
if ([FBSDKAccessToken currentAccessToken]) {
             [login logOut];
        }

and issue was user was trying to login as another user as suggested by @Vineeth Joseph

Check the state of your FBSession:

isOpen
Indicates whether the session is open and ready for use.
@property (readonly) BOOL isOpen;
Declared In: FBSession.h

https://developers.facebook.com/docs/reference/ios/3.0/class/FBSession/

304 indicates that nothing has changed. Probably you are somehow already authenticated and so getting nil with 304 indicating nothing has changed.