PlayFab mainly provides two types of APIs, which are Classic APIs and Entity APIs. Classic APIs are Client APIs, Server APIs and etc. In terms of Entity APIs, they are comparatively new and new features like Multiplayer 2.0 , entity group and those who will require entity token will use the Entity Model.
In the classic API, we will only use PlayerId for reference, and there are many entity types in the new Entity Data Model, please refer to Available built-in entity types. PlayerId equals to master_player_account, meanwhile for most of Entity APIs, title_player_account is required for reference. And it is why Client API GetUserData can only use PlayerId (or master_player_account) for the call.
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