QuickChart Chart.js unexpected identifier

Question

I want to send a dynamically generated image, created with quickChart, with email in php. For testing i created the chartConfig in the quickChart Sandbox, everything is fine. When i copypaste the config to my php an start it, then i get ChartError: Error: unexpected identifier - 18:26. I don't get it what the problem is. Here is my code:

$chartConfig = '{
  type: "horizontalBar",
  data: {
    labels: ["Sei perfekt", "Streng dich an", "Sei schnell", "Sei gefaellig", "Sei stark"],
    datasets: [
      {
        backgroundColor: ["#97cc64", "#97cc64", "#97cc64", "#97cc64", "#97cc64"],
        data: [26, 30, 25, 26, 25],
        barThickness: 30,
      },
      {
        backgroundColor: ["#ffd050", "#ffd050", "#ffd050", "#ffd050", "#ffd050"],
        data: [null, 10, null, null, null],
        barThickness: 30,
      },
      {
        backgroundColor: ["#fd5a3e", "#fd5a3e", "#fd5a3e", "#fd5a3e", "#fd5a3e"],
        data: [null, 5, null, null, null],
        barThickness: 30,
      },
    ],
  },
  options: {
    legend: {
      position: "bottom",
      labels: {
        generateLabels: (chart) => [
          {
            text: "Gesund",
            fillStyle: "#97cc64",
          },
          {
            text: "Uebermaessig",
            fillStyle: "#ffd050",
          },
          {
            text: "Negativ",
            fillStyle: "#fd5a3e",
          },
        ],
      },
    },
    scales: {
      xAxes: [
        {
          stacked: true,
          ticks: { min: 0, max: 50, display: true },
          gridLines: { display: true },
        },
      ],
      yAxes: [{ stacked: true, gridLines: { drawBorder: false } }],
    },
  },
}';
 
$chartUrl = 'https://quickchart.io/chart?w=500&h=300&c=' . Urlencode($chartConfig);

$chartUrl is then added to my html. But instead the chart, i get the error image in the email.

Thank you!