Walmart expects their sellers to acknowledge the received orders. Once you acknowledge the order and update your inventory, Walmart will know that you got the order and display the available item quantity correctly.
If you do not acknowledge your orders, this may lead to underselling and outdated product data. The item quantity displayed on Walmart will be lower than the actual inventory count.
You can acknowledge each Walmart order in your Seller Center manually. Or take a less time-consuming path and make M2E Pro acknowledge all your Walmart orders automatically.
To do that, check whether the automatic Magento order creation is enabled in your Account settings: Walmart > Configuration > Accounts > selected Account > Orders:
With this option enabled, M2E Pro will automatically acknowledge your Walmart orders and import them into Walmart > Sales > Orders section. The corresponding Magento order will be created per each Walmart order. As a result, Magento Product stock will be reduced appropriately.
Walmart orders that have not been acknowledged yet are displayed as Created in the M2E Pro order grid (Walmart > Sales > Orders):