I was able to use the free plotly.js library to render the chart in memory, then when finished grab a base64 encoded stream of the jpg or png image (i think). Here is the bit of the flow I used to test it with a few static data points (of course it only works when the /red/ui page is active in the browser):
The issue was in the .Net Core RESTful service this Angular app was calling. It was returning a JsonResult which had the expected object under a "Value" element. The original Pascal casing of the class in Angular was probably also an issue originally.