Blocked in GetOculusIdentity when startup app by test user account

I upload my apk developed by UE4 engine to AppLab, and have followed all the steps outlined in the "Test Users" document. In the BeginPlay of GameMode blueprint, I have successfully passed the VerifyEntitlement process. However, when I call GetOculusIdentity, there is no response whether it's a Success or Failure. Could anyone please suggest what the possible issue might be?