Hello,
The SDK is not compatible with Unity 2019, but you can make it work very easily. Open the file Plugins/BuildCheck.cs, and change that line (line 186) :
if (Application.unityVersion.StartsWith("2017.") || Application.unityVersion.StartsWith("2018."))
by
if (Application.unityVersion.StartsWith("2017.") || Application.unityVersion.StartsWith("2018.") || Application.unityVersion.StartsWith("2019."))
Your application is not working with all versions of Unity 2019, including beta!
Cheers