Add horizontal line to AmCharts4 Dumbbell plot

Found the way here.

var range = valueAxis.axisRanges.create();
range.value = 1000;
range.grid.stroke = am4core.color("#396478");
range.grid.strokeWidth = 2;
range.grid.strokeOpacity = 1;
range.grid.strokeDasharray = "6,3";

This works for other kinds of charts, of course.