Phaser Tiled Tilemap Parsing error

Phaser 3
1

I’m making a Tilemap system using Tiled for my game. But Phaser can’t parse the Tilemap.
It throws this error:

Uncaught TypeError: Cannot read property ‘2’ of undefined
at AssignTileProperties (phaser.js:132071)
at ParseJSONTiled (phaser.js:132012)
at Parse (phaser.js:131876)
at ParseToTilemap (phaser.js:65828)
at GameObjectFactory.tilemap (phaser.js:203413)
at C1Scene.create (C1Scene.ts:66)
at SceneManager.create (phaser.js:98721)
at SceneManager.loadComplete (phaser.js:98633)
at LoaderPlugin.emit (phaser.js:1908)
at LoaderPlugin.loadComplete (phaser.js:193262)

This is the loading code:

create(){
this.bg = this.add.image(this.game.renderer.width / 2, this.game.renderer.height / 2, “skyGradient”);

    let mainmap = this.add.tilemap("mainmap");
    let terrain = mainmap.addTilesetImage("MainTerrainTileset", "terrainTileset");

    // Terrain Layers
    let terrainLayer1 = mainmap.createLayer("Tile Layer 1", [terrain], 0, 0);//.setDepth(-1);
    
    // More code here...
}

“mainmap” is this.load.tilemapTiledJSON(“mainmap”, “./assets/maps/TerrainTilemap.json”);