(com.facebook.sdk.login error 304.) Error with FBSDK 4.2

Swift 4 update :

Everytime you perform something like this

    FBSDKLoginManager().login(withReadPermission: ["email"], from: self) { (result, error) in  // Check for error and then login }

    //insert this code before the **Login code:** 
    FBSDKLoginManager().logOut()

and it should work fine :)

This may because of previous login token not cleared.So before login just logout.

NSString *const read_actions = @"email";
FBSDKLoginManager *loginManager = [[FBSDKLoginManager alloc] init];
[loginManager logOut];
[loginManager logInWithReadPermissions:@[read_actions]
                               handler:^(FBSDKLoginManagerLoginResult *result, NSError *error) {
                                   if (error) {
                                       NSLog(@"Login Failed with error: %@", error.localizedDescription);
                                   }
                                   else if (result.isCancelled) {
                                       NSLog(@"Login Failed due to Cancel");
                                   } else {
                                       if ([result.grantedPermissions containsObject:read_actions]) {
                                           NSLog(@"Permission granted");
                                        }
                                   }
                               }];