You need to add ```RhinoDocument.Views.Redraw();``` to the your ``drawMethod``:
```cs
private void RunScript(ref object A)
{
  var = new Rhino.Input.Custom.GetPoint();
  getPt.Get();
  basePt = getPt.Point();
  getPt.DynamicDraw += drawMethod;
  getPt.Get();
  display.Dispose();
}
// <Custom additional code> 
Rhino.Display.CustomDisplay display = new Rhino.Display.CustomDisplay(true);
Point3d basePt = new Point3d();
void drawMethod(object sender, Rhino.Input.Custom.GetPointDrawEventArgs e)
{
  display.Clear();
  display.AddLine(new Line(basePt, e.CurrentPoint), System.Drawing.Color.DodgerBlue, 10);
  RhinoDocument.Views.Redraw();
}
// </Custom additional code> 
```
[GetPoint.gh|attachment](upload://mPIGYip5QY1AkHrcjsaaSQ45hMI.gh) (2.2 KB)