Download pixel art drawing as .png in PhaserJS

I need to download the created pixel drawing from this Phaser example as a .png image via FilesSaver.js but the canvas returns null.

Error:

Uncaught TypeError: Cannot read properties of null (reading 'toBlob')

This is the save function:

function save() { 
var canvasX = document.getElementById("canvas");
canvasX.toBlob(function(blob) { saveAs(blob, "image.png"); }); }

drawingArea: (PhaserJS 2)

function createDrawingArea() {

    game.create.grid('drawingGrid', 16 * canvasZoom, 16 * canvasZoom, canvasZoom, canvasZoom, 'rgba(0,191,243,0.8)');

    canvas = game.make.bitmapData(spriteWidth * canvasZoom, spriteHeight * canvasZoom);
    canvasBG = game.make.bitmapData(canvas.width + 2, canvas.height + 2);

    canvasBG.rect(0, 0, canvasBG.width, canvasBG.height, '#fff');
    canvasBG.rect(1, 1, canvasBG.width - 2, canvasBG.height - 2, '#3f5c67');

    var x = 10;
    var y = 64;

    canvasBG.addToWorld(x, y);
    canvasSprite = canvas.addToWorld(x + 1, y + 1);
    canvasGrid = game.add.sprite(x + 1, y + 1, 'drawingGrid');
    canvasGrid.crop(new Phaser.Rectangle(0, 0, spriteWidth * canvasZoom, spriteHeight * canvasZoom));

}

How to get the data of the drawing to create a .png out of it?

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