Electron Builder Appx: The package manifest is not valid

I was trying to package my app with Electron Builder as an Appx file, to publish it in the Windows Store. But I keep on getting this strange error which says that my manifest file is not vailed:

MakeAppx : error: Package creation failed.
MakeAppx : error: 0x80080204 - The specified package format is not valid: The package manifest is not valid.

Actually, I have a working AppxManifest.xml but can't use it in electron builder. My identity variables should be right too (I used it in some other tool and published successfully). So I'm kinda stuck here.

This is my package.json

{
  "name": "***",
  "version": "1.0.1",
  "description": "Made with love <3",
  "main": "index.js",
  "scripts": {
    "start": "electron .",
    "pack": "electron-builder --dir",
    "dist": "electron-builder"
  },
  "author": "***",
  "license": "All Rights Reserved",
  "dependencies": {
    "knex": "^0.21.6",
    "sqlite3": "^5.0.0"
  },
  "devDependencies": {
    "electron": "^10.1.2",
    "electron-builder": "^22.9.1"
  },
  "build": {
    "productName": "***",
    "appId": "***.com",
    "directories": {
      "buildResources": "assets"
    },
    "win": {
      "icon": "assets/icon.ico",
      "target": [
        "nsis",
        "appx"
      ]
    },
    "nsis": {
      "oneClick": false,
      "perMachine": true,
      "allowToChangeInstallationDirectory": true
    },
    "appx": {
        "identityName": "NumberPublishername.Appname",
        "publisher": "CN=LongNumber",
        "publisherDisplayName": "Publishername",
        "applicationId": "Appname"
    }
  }
}

The problem was this line Made with love <3, the < character is not allowed there because the XML is invalid. Sadly the console doesn't say what is wrong.