The availability attribute only has four accepted values:
'in stock': Include this value if you are certain that it will ship (or be in-transit to the customer) in 3 business days or less. For example, if you have the item available in your warehouse.
'available for order': Include this value if it will take 4 or more business days to ship it to the customer. For example, if you don’t have it in your warehouse at the moment, but are sure that it will arrive in the next few days. For unreleased products, use the value 'preorder'
'out of stock': You’re currently not accepting orders for this product.'
'preorder': You are taking orders for this product, but it’s not yet been released.
When to include: Required for all items in feeds targeting the US, Japan, UK, Germany and France. Recommended for feeds targeting all other countries (although might become required in the future).
Type Four predefined values accepted:
'in stock'
'available for order'
'out of stock'
'preorder'
Text/Tab delimited in stock
XML <g:availability>in stock</g:availability>
Important:
You need to clearly indicate the availability of an item on the item's landing page by either explicitly noting the status (so that it's clear which of the above values describe the availability of the item) or mention how many days it will take for the item to be shipped. (Note: It is acceptable to include 'available for order' in your feed and note "out of stock" on your website.)
Items that are no longer sold have to be removed from the feed entirely.
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