The Problem
During the order placement and fulfilment processes, Magento's MSI implementation will not decrement stock on order placement - it will only do so on order shipment and refund.
Solution
Install the module and follow the additional steps from the official documentation
# composer req ampersand/magento2-disable-stock-reservation
This module disables the inventory reservation logic introduced as part of MSI in Magento 2.3.3 - see magento/inventory#2269 for more information about the way MSI was implemented, and the issues that can happen with external WMS integrations.
Source: https://github.com/AmpersandHQ/magento2-disable-stock-reservation
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