Make sure your buylist setting is on. This setting can be found via Restock > Buylist Settings
2. Make sure the categories holding the products are not hidden. You can check if a category has hidden the buy list products under Inventory > Category and then select a category. Look for the check boxes next to "Hide category from the buy list"
Note - If the parent category hides the category, all children categories of this will also hide the products.
3. Make sure for your product, the opt qty is greater than the actual qty of the product, especially the variant qty of the product.
4. Make sure the product has a buy price. If your products do not have a buy price, they will not appear on the website or POS.