TypeLoadException Unity Ads v2.3.0 in Unity 5.4.4p1 iOS

It's been a while since I updated my Unity Ads (v2.0.x) Dec. 2017 (running Unity 5.4.4p1). After doing the update, everything works fine in the Editor and on Android, but throws an exception on iOS at initialization (new iPad, 5c, 6).

Looks like it stems from UnityEngine.Advertisements.Purchasing.Initialize -> UnityEngine.Advertisements.iOS.Platform.UnityAdsPurchasingInitialize()

Checks:
isInitialized=true
Version=2.3.0
iSupported=true

With the advent of Unity Ads Promo, is an update to...

TypeLoadException Unity Ads v2.3.0 in Unity 5.4.4p1 iOS