You can use this API to acknowledge an entire order, including all of its order lines. Walmart requires a seller to acknowledge orders within four hours of receipt of the order, except in extenuating circumstances.

The response to a successful call contains the acknowledged order.

In general, only orders that are in a Created state should be acknowledged. As a good practice, acknowledge your orders to avoid underselling. Orders that are in an Acknowledged state can be re-acknowledged, possibly in response to an error response from an earlier call to acknowledge order. Orders with line items that are shipped or canceled should not be re-acknowledged.