The answer you provided is fine, but is just using an array as a json array instead of a json object. You can refer to json.org for specification. The one that was wrong was what you wrote in your initial question, which was just plain text.
In summary, this is a JSON array:
[ "Ford", "BMW", "Fiat" ]
This is a JSON object, that can contain arrays:
{
"name":"John",
"age":30,
"cars":[ "Ford", "BMW", "Fiat" ]
}
A JSON file can contain multiple arrays, or objects.