FBSDKLoginManager logInWithPublishPermissions always returns isCancelled=YES

I am having trouble figuring out how to log a user into my app. [FBSDKAccessToken currentAccessToken] is nil, so I am calling:

[[[FBSDKLoginManager alloc] init] logInWithPublishPermissions:@[@"publish_actions"] handler:…];

as per the included sample project. This switches to the Facebook app, but the message says "You have already authorized App Name.". I click OK and it goes back into the app, but grantedPermissions and declinedPermissions are both nil on the result, and isCancelled is YES. [FBSDKAccessToken currentAccessToken] is still nil.

I can't figure out how I'm supposed to get currentAccessToken to be filled in. It seems to me the call to logInWithPublishPermissions should do that, but it isn't.