Watchkit cannot use iCloud?

Refer to https://stackoverflow.com/questions/42037211/watchkit-extension-cannot-read-from-icloudhttps://developer.apple.com/contact/#!/topic/SC1102/subtopic/30014/solution/select

When I try to synchronize data between iOS and watchOS, iCloud is not working.

When I use

NSFileManager *fm = [NSFileManager defaultManager];
id token = [fm ubiquityIdentityToken];

to get iCloud token, it will get a error code 4009 and get nil from ubiquitIdentityToken.

I've turn on iCloud settings on Capabilities page on watchOS extention target.

Does watchkit not support iCloud service but be with the setting page?

Thank you.