How to only show products from a specific category?

Question

Ì created a grouped product and some simple products associated with it on my fresh installed Magento project. Then I created a new category "kleber_category" and associated the grouped product to it.

Then I created a new site "kleber" and a link to it on the homepage.

How can I display all grouped products from the category "kleber_category" on the page "kleber"?

What I've tried:

1. Find out the id of the category (3)
2. Add the following line to the content section of the page "kleber":

{{block type="catalog/product_list" category_id="3" template="catalog/product/list.phtml"}}

Result:

The page "kleber" in the frontend shows:

"There are no products matching the selection."

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UPDATE

I changed the quantity settings from the grouped object to this, but it made no difference:

Enable Qty Increments: Yes

Stock availability: In Stock

Answer 1

I figured it out. It does only work if the category is inside the "Default Category". It works after moving the folder to the "Default category".

Note: You can drag and drop it in.