The following steps needs to be done on all three sites (Germany, Austria, Switzerland)

Open up the CMS Content Sync Drupal configuration pages

and go to the Pools tab. Next we will create the four Pools that are needed to fulfill our requirements: DACH, Germany, Austria and Switzerland.

To create the first pool click on "Add Pool" at the top of the page. On the following screenshot you can see the configuration for Site - Germany, Pool - DACH.

Sync Core URL
The Sync Core URL will be provided by the Edge Box GmbH to you. If you do not have a Sync Core URL yet, feel free to contact us:

After hitting Save, you will be redirected to the export page for the pool. Wait until it has finished before you continue:

You will see a success message once it's finished:

If you see any errors here, you probably entered an incorrect Sync Core URL. In that case re-enter the correct URL and wait for the export to finish.

Repeat the creation process for the pools so that the required pools are available on the sites they belong to.

Keep in mind the given requirements
Germany belongs to the pools: DACH, Germany
Austria belongs to the pools: DACH, Austria
Switzerland belongs to the pools: DACH, Switzerland

So that you end up with the following pool setups.