Sometimes, an item might be out of stock even though it seems that the corresponding Amazon item is in stock. If you've checked all the things in the other OOS article but still can't figure out why, you might want to try this.
1. Go to the page of the Amazon item.
2. Click on the envelope icon on the page
3. A popup will show up. The ASIN within this popup, shown highlighted, is the correct ASIN.
Sometimes, this ASIN will be different from the ASIN you see on the URL or on the page. In spite of that, the one in the pop-up box is the correct ASIN. If this is the case - that your OOS item has a different ASIN than this one - update your Zinc tag, or delist the item and re-list the item with the new ASIN.