C# Signature:

[DllImport("user32.dll", SetLastError = true, CharSet= CharSet.Auto)]
public static extern int MessageBox(int hWnd, String text, String caption, uint type);

VB.Net Signature:

Please Add Some!

Alternative Managed API:

System.Windows.Forms.MessageBox (WinForms)

System.Windows.MessagBox (WPF)

Notes:

https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-messagebox