[Chartjs]-Where put "multiTooltipTemplate" in Chart.js v2.x

Your options object should be

...
options: {
  tooltips: {
    callbacks: {
      label: function(tooltipItem, data) {
        var datasetLabel = data.datasets[tooltipItem.datasetIndex].label || '';
        return datasetLabel + ' : ' + tooltipItem.yLabel + ' €';
      }
    }
  }
}
...