the item on our site is not out of stock.
The user adds to the cart. When the user checks out, it displays the item is out of stock.
Does anyone know why this happens?
It’s hard to say without seeing your settings but if you’ve set up multiple locations it could be your products are not stocked in a location that is set to serve the online store.
https://help.shopify.com/en/manual/locations/setting-up-your-location-fulfillments
thank you for reaching out. It’s a software glitch and it was fixed.