You need to write the ID of the category in admin panel (line “Categories:”), not the category name. Try inserting the desired category ID and see if it helps.
You can find out the category ID’s by going to “Portfolio -> Portfolio categories”. Hover the desired category name, and in the link that will open, find the part e.g.
&tag_ID=13. The last number is the ID of a category (in this case, 13).