«SyntaxError: "invalid property id"» while editing the root composer.json file

Outdated Questions
8

The easiest solution for you is just to follow the Step 3 of the my installation instruction.
The instruction states:

Change the repositories section to the following:

"repositories": [
    {
        "type": "composer",
        "url": "https://repo.magento.com/"
    }
    ,{
        "type": "composer",
        "url": "https://mage2.pro"
    }
],

A more complex solution is to use the key-value notation:

"repositories": {
	"0": {
		"type": "composer",
		"url": "https://repo.magento.com/"
	},
	"1": {
		"type": "composer",
		"url": "https://mage2.pro"
	}
}