It appears that in 2017.3p2 or possibly p1 (I skipped p1) that WWW.SendRequest no longer exists...
Apparently Unity decided to change the method name to just "Send" for whatever reason...
In PlayFabUnityHttp.cs (PlayFabSdk/Shared/Internal/PlayFabHttp) line # 68 this needs to be updated, I checked the GitHub repo, and it doesn't appear to be updated yet.
As us the SDK causes a compile error in 2017.3p2