There is no limit to the pre-order quantity by default. It means that a customer can pre-order an unlimited quantity of products.
You can set up a pre-order quantity limit, which can be pre-ordered for a specific variant of the product (in the case of applying the settings to the whole product(s) - for each variant).
If the pre-order quantity limit is 10, it is reached when the inventory value is -10.
Set up pre-order quantity limit for one variant or product
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