Callback Vungle.onInitializeEvent is not called on UWP build

I have set up vungle ad for UWP build by Unity. The callback Vungle.onInitializeEvent is not called after calling function Vungle.Init.

And I have tried log many other callbacks like Vungle.onLogEvent, Vungle.onErrorEvent, Vungle.onWarningEvent, Vungle.onAppTrackingEvent to check if any error is happening => then all above callbacks are not called.