In some situations, your online store won't display purchase tools for certain products, which makes it impossible to add them to the shopping cart. This article discusses the reasons why purchase tools might not be displayed for a product.
1) The product's sales were set to stop if the product runs out of stock
If the product's stock balance is limited and you've checked the option on the product card for the product's sales to stop when it runs out of stock, it won't be possible to purchase the product from your online store.
2) No price has been set for the product or its variation
If no price has been set for the product, customers won't be able to buy it from your online store. If the product has variations, you can leave the main product unpriced, but you must specify prices for all of its variations.