I appreciate that you have included a screenshot of the message you are seeing, as that is very helpful. If Facebook has detected that your product(s) is not available on your online store or is password protected, this could mean one of two things.
First, I would suggest making sure that your store is not password protected. You can quickly navigate to Online store > Preferences to find the password page section. We will need to ensure that enabled password is not selected. I took a screenshot from my test store to show you the section I am referring to:
Second, if you can confirm that your store is not password protected, this message would be due to the fact that your product(s) are not available on your online store. You can add your products to a collection and then add the collection to your online store. Once that has been completed, it may take a couple of minutes for Facebook to sync with the new changes made.