The content directory type 'sync' does not exist

They really need this in the readme...

You need to add the following to your sites settings file:

global $content_directories;
$content_directories['sync'] = 'whatever-base-path-you-have/content_sync';

I had done that (Im assuming from OP), but maybe I did not specify global.

Create content directory and sync directory inside it, in your drupal installation root folder.

Add the following lines to your settings.php file

global $content_directories;
$content_directories['sync'] = $app_root.'/../content/sync';

This should fix your problem

Setting back to active, there is nothing to review unless changes (code or docs) are proposed.

In the latest version of this module config in settings.php should look like this:

$settings['content_sync']['sync'] = '../content/sync';