How to login to Google Play not on startup but later

Hi,
how can I login to Google Play not on startup but later, for example on login button clicked?
My code for that doesn’t work:

IOnlineSubsystem* OnlineSub = IOnlineSubsystem::Get("GooglePlay");
IOnlineIdentityPtr IdentityInterface = OnlineSub->GetIdentityInterface();		
IdentityInterface->AutoLogin(0);

After call AutoLogin nothing happened…

Could you help me?
Thank you.

Look at examples, Match3 puzzle is a nice one to look at.
You can simply use blueprints to login and logout of GooglePlay/GameCenter.