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-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).

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Set up pre-order quantity limit by default

1. Go to Settings > Default settings 
   
2. Click Edit
   
   
3. Set up pre-order quantity limit
   
4. Click Save

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