How to add Legend in Highcharts in Angular-8

I am not able to add legend in my project as it throws error.
I have even enabled showInLegend: true in in plotOptions in my project, but I am not sure how to enable it for particular things.

For example in my project I want to enable Legends for the colored dots being plotted(anomalies) & thresholds in the variable data.

https://stackblitz.com/edit/highchart-highstock-28rsqp?file=src/app/app.component.ts

Source: Angular Questions