High charts AddAnnotation is not a function for dynamic adding

I currently have a working highcharts line chart (version 6.0.3). I have multiple series where I am live updating. I am looking to add annotations to the points, linked by an ID, that follow the point as I add more dynamically. For example, I add it to point at index 3, and as I add more, the annotation shuffles to the left with the point at array[3].

The problem I currently have is dynamically adding annotations. Here is how my chart options are setup:

  function createTrendTool() {
            _trendToolChart = Highcharts.chart('trendToolContainer', {
                chart: {
                    type: 'spline',
                    zoomType: 'x',
                    panning: true,
                    panKey: 'shift'
                },
                tooltip: {
                    formatter: function () {
                        var unit = this.series.userOptions.Unit;
                        if (unit) { unit = ' ' + unit; }

                        var s = '<b>' + this.series.name + '</b>';
                        s += '<br/>' + moment(this.x).format('MMM D YYYY HH:mm:ss') +
                            '<br/>' + this.y + unit;
                        return s;
                    }
                },
                annotations: [{
                    labelOptions: {
                        backgroundColor: 'rgba(255,255,255,0.5)',
                        verticalAlign: 'top',
                        y: 15
                    }, 
                    labels:[]
                }],
                title: {
                    text: 'Trending Signals'
                },
                credits: false,
                yAxis: {
                    title: {
                        text: 'Values'
                    }

                },
                xAxis: {
                    title: {
                        text: 'Time'
                    },
                    type: 'datetime'
                },
                legend: {
                    layout: 'vertical',
                    align: 'right',
                    verticalAlign: 'middle'
                },

                plotOptions: {
                    series: {
                        label: {
                            connectorAllowed: true
                        }
                    }
                },
                responsive: {
                    rules: [{
                        condition: {
                        },
                        chartOptions: {
                            legend: {
                                layout: 'horizontal',
                                align: 'center',
                                verticalAlign: 'bottom'
                            }
                        }
                    }]
                }

            });

            _trendToolChart.showLoading("Loading...");
        }

The chart setups without any issues. On retrieving data from my API, I want to dynamically add an annotation, so I grab the series from my chart and then try to add the annotation with this:

     function addAnnotationToChartPoint(point, annotationText) {
        _trendToolChart.addAnnotation({
            linkedTo: point.Id,
            title: annotationText
        });
    }

The point.Id is a guid, and the annotationText is a string.

But when I call the function I get this error:

TypeError: _trendToolChart.addAnnotation is not a function at addAnnotationToChartPoint (.js:865)

I can see annotations listed in the options and userOptions array on the chart, but the function isn't there. Is there something I need to setup first?