This might be because you haven't granted the correct Channel access or it has been unlinked to your performances.
When creating your Product, you must enable Channel access via the Visibility tab of the product.
Then when creating your Product Price Table, Channels have to be given access to your Variants in the same way as for tickets. If they're not granted access here, then the Product will show in the purchase flow, but will not be available to be added to the basket, as no prices will be available on that Channel.