The most important thing to ensure that your spa item is private/hidden but still works, is to tick BOTH of the boxes below.

If only 'Visible via direct URL' is ticked, the direct link will not work. Although you will have hidden this item from your public listing, you have not published it so it does not exist anywhere publicly, even via the direct URL.

You must have both ticked to create a working, but private/hidden, spa item.

To find out the spa item's URL, click the three dots to the right of the spa item's name and click 'view' to open the direct URL in a new tab.

From there you can copy the URL and share to the targeted audience.