@elitriona,

It seems like you are not rendering the chart after updating the datapoints on ajax request. Calling chart.render() after updating the datapoints will work fine in your case. Please take a look the code snippet below for the same.

$.getJSON('https://trionacgm.fly.dev/api/v1/entries.json?count=12', function(data) {
  chart.options.data[0].dataPoints = [];
  $.each(data, function(key, value) {
    chart.options.data[0].dataPoints.push({
      x: (value['date']),
      y: Number(value['sgv'])
    });
  });
  chart.render();
});

Also, check out this JSFiddle for complete working code.

—-
Manoj Mohan
Team CanvasJS