The category_in option allows you to show only the entries assigned to the supplied categories, by ID.The category ID can be found on the Connections : Category admin page as shown in this screen capture.
NOTE: This attribute is an operational AND function. An entry will only be shown if it is in all of the specified categories
or one of their children categories.
/* * To show only the entries that have been assigned to the listed category IDs. */ [connections category_in='1,3,9']