Out of Stock Purchasing
When a customer adds a quantity of product to their basket that is greater than what you have in stock, depending on what your settings are, the customer will see this message:
Products marked with *** are out of stock.
Items not in stock will be placed on backorder.
Your customer can still finish checkout with out of stock items.
You can choose to allow checkout with backorder status or you can choose to have the customer revise the quantity in their basket, in which case, if the customer has too many items in their basket the customer will see this message:
Products marked with *** are out of stock or there are not enough in stock to fill your order.
Please change the quantity of products marked with (***). Thank you
Your customer will need to adjust the quantity to what is in stock before they can finish checkout.
This setting can be found in
admin > configuration > stock > Allow Checkout
Allow customer to checkout even if there is insufficient stock
set this to true or false