An 855 Purchase Order Acknowledgment is a formal response sent by a supplier to a buyer confirming receipt and acceptance (or conditional acceptance) of a purchase order. The supplier sends this transaction to the buyer to provide visibility into order status, acknowledge line items, and communicate any modifications to pricing, quantities, delivery dates, or terms. Key segments include the BAK (Beginning Segment for Purchase Order Acknowledgment), which establishes the acknowledgment type and related purchase order reference; the PO1 loop, which contains baseline item data and allows the supplier to confirm, modify, or reject individual line items; and the ACK loop, which provides explicit acknowledgment status for each line with corresponding dates and monetary amounts.

For example, when TechSupply Inc. receives a purchase order from RetailCorp for 500 units of wireless keyboards at $45 each with a requested delivery date of March 15, TechSupply responds with an 855 transaction. In the BAK segment, TechSupply identifies the acknowledgment as “Accepted” and references RetailCorp’s original order number. Within the PO1 detail loop, TechSupply confirms the 500-unit quantity and $45 unit price. However, if inventory constraints exist, the ACK segment for that line item can indicate “Accepted with change,” and the LDT (Lead Time) segment can communicate that delivery will occur on March 22 instead. The 855 thus provides RetailCorp with a clear, machine-readable confirmation of what the supplier will deliver and when.