Unity Test ads not showing up after build and run to Android device

Do you have a placement called “test” in your Unity Dashboard? Please provide the output of your Debug.Log statements on the device, they will be in the log. Your first debug statement in Start() will of course be false, as you haven’t initialized ads yet

Debug.Log("Unity Ads initialized: " + Advertisement.isInitialized);

This may help also:

https://unityads.unity3d.com/help/unity/integration-guide-unity