Play Games C++ SDK where is gpg::LeaderboardCollection::FRIENDS?

Question

I'm using the latest Play Games C++ SDK Version 3.1.0 in my games and use it to display leaderboards using my own UI. I want to display my Friend's scores but gpg::LeaderboardCollection::SOCIAL (value 2) has been deprecated and ScorePageToken() returns nothing if I use that constant there. However, if I display leaderboards using Google's UI then it's possible to filter leaderboads by Friends and it appears that in other SDKs there's now a LeaderboardCollection::FRIENDS constant that has a value of 3. I've tried passing 3 to ScorePageToken but it doesn't help. I think internally this function converts the 3 to a string. Is there any way to use the REST API via the login credentials that the C++ SDK has returned as it doesn't seem like this C++ SDK is updated regularly (last update Nov 2019) ?