Parse error: syntax error, unexpected ':', expecting ']'

Вот фрагмент кода:

$http = new GuzzleHttp\Client;
$response = $http->post('https://anilist.co/api/v2/oauth/token', [
    "form_params" => [
        "grant_type" => "authorization_code",
        "client_id" => "1400",
        "client_secret" => "2fIcQ0M3iHgrh63B09oh8z521bnGpjkw3LxvAKeh",
        "redirect_uri" => "https://example.com/",
        "code" => $code
    ],
    "headers" => [
        "Content-Type": "application/json",
        "Accept": "application/json"
    ]
]);
return json_decode($response->getBody())->access_token;

Ошибка Parse error: syntax error, unexpected ':', expecting ']'