.netcore app throws SEHException exception when referencing c++ dll

Question

I have created a c++ dll. I'm using System.Runtime.InteropServices. First I tested the dll with a .netcore console application and it worked successfully. When attempting to reference it with a .netcore application, I get a SEHException: External component has thrown exception: Here is how I'm referencing the dll

using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Runtime.InteropServices;


namespace WpfApp1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {

        [DllImport(@"C:\Users\source\repos\Digital\x64\Debug\DigitalDrive.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern int add(int a, int b);
        [DllImport(@"C:\Users\source\repos\Digital\x64\Debug\DigitalDrive.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern void start();
        public MainWindow()
        {           
            start();            
            InitializeComponent();
        }
    }
}