Custom Field "category-include" not working

if you read these directions, it will tell you how to set up a portfolio page on this theme that I have:

Portfolio pages can be created with the help of page templates

1. Log in to your WordPress Administration Panel (Dashboard).

2. Click the Pages tab on the right

3. On the next page, cick the Add New tab

4. Type in your page name, for example Portfolio page

5. Under the Page Attributes, select a Parent for your page

6. Select your page template ( Portfolio full or Portfolio in the Page Attributes drop-down menu)

7. Under the Custom Field tab, add a new field called “category-include” (or just select it under the Name drop-down menu)

category-include – name of the category that is displayed on this Portfolio page (available only for the Portfolio page template) You need to use the slug of the category here (go to Portfolio -> Portfolio Categories and copy the slug from the tab on the right)

9. With that done, click the Update button

If you look were it says category-include I have done everything it says there and also watched a video. but on my template the category-include custom field will not work, no matter what I do. Does anyone have any ideas why it will not work??