--- title: "What Is an EDI 855 (Purchase Order Acknowledgment)?" url: https://www.uncap.com/glossary/edi-855 author: "Denis Dyli" published: 2026-10-11 updated: 2026-10-11 summary: "An EDI 855 is the X12 Purchase Order Acknowledgment transaction set: the electronic document a seller sends back to a buyer after its system has processed an EDI 850 purchase order. It may affirm the order or indicate changes to it. X12 also allows it as notice of a vendor generated order that was prearranged with the buyer." --- # What Is an EDI 855 (Purchase Order Acknowledgment)? > An EDI 855 is the X12 Purchase Order Acknowledgment transaction set: the electronic document a seller sends back to a buyer after its system has processed an EDI 850 purchase order. It may affirm the order or indicate changes to it. X12 also allows it as notice of a vendor generated order that was prearranged with the buyer. **EDI 855 (Purchase Order Acknowledgment)**: An EDI 855 is the X12 Purchase Order Acknowledgment transaction set: the electronic document a seller sends back to a buyer after its system has processed an EDI 850 purchase order. It may affirm the order or indicate changes to it. X12 also allows it as notice of a vendor generated order that was prearranged with the buyer. ## How it works In X12's supply chain flow, the 850 and the 855 together make up the purchase order process, which establishes the legal contract between the parties about the purchase. The 855 is reported back from the seller's purchase order system after the 850 data has been processed. Two other documents handle what happens next. The buyer can request a change to a previously submitted order with an 860, and the seller can accept, reject or modify an order with an 865. Partners that have not implemented the 860 or 865 may allow several rounds of the 850 and 855 under the same purchase order number, up to an agreed cut-off point. **Where the EDI 855 sits in the order cycle** ### 1. 850, Purchase order The buyer's system places the order. With the 855, it makes up the purchase order process. ### 2. 997, Functional acknowledgment The seller's system confirms receipt of the 850 and that it can be used. ### 3. 855, Purchase order acknowledgment The seller reports back after processing the 850, affirming the order or indicating changes. ### 4. 856, Ship notice/manifest The delivery process advises the buyer about product that is being shipped. ### 5. 810, Invoice The seller transmits an invoice to the buyer requesting payment. ## What it contains The segment detail below comes from X12's own sample 855s, published for the aerospace industry in X12 version 004010. X12 says these examples are educational and do not override its standards or implementation guides. - BAK: marks the document as an acknowledgment, gives the acknowledgment type and names the purchase order number and date being acknowledged. The samples use AT (accepted, no detail), AD (acknowledge with detail), AC (acknowledge with detail and change) and RJ (rejected, no detail). - PO1: each line as the buyer ordered it, with quantity, unit price and part number. - ACK: the line item status code and certain change information. Codes in the samples include IA (accepted, no changes), IQ (accepted, quantity changed), IP (accepted, price changed), DR (accepted, date rescheduled) and IR (rejected). - CTP and SCH: a changed price, and shipment schedule dates where the partners have agreed to include them. - CTT: the number of line items in the acknowledgment. ## Example A buyer's 850 orders two lines: 100 units at $4 ($400) and 50 units at $10 ($500), for $900 in total. The seller can supply every unit of the first line but only 30 units of the second. Its 855 uses acknowledgment type AC, acknowledge with detail and change. The first line's ACK segment says IA, accepted. The second line's ACK segment says IQ, accepted with the quantity changed to 30. The acknowledged value is $400 + (30 x $10) = $700, and the CTT segment counts 2 line items. In X12's own sample with changes, the supplier treats the order as on hold until the buyer replies with an 860 that accepts the changes or cancels the order. ## On Shopify Shopify's orderCreate mutation is meant for orders that aren't created through the standard checkout, such as orders imported from an external system or created for wholesale customers. The order keeps the buyer's PO number in its poNumber field, which Shopify describes as typically provided by business customers who require a PO number for their procurement. When the seller changes an order, apps can edit it through the GraphQL Admin API: add items, alter line item quantities, or remove a line item by setting its quantity to zero. Only unfulfilled line items can be edited. The orders/edited webhook fires whenever an order edit is completed. ## How Uncap helps Uncap's [Shopify EDI integration guide](/post/shopify-edi-integration) is direct about the risk: if the EDI connector is not monitoring for new Shopify orders and triggering acknowledgments automatically, a manual process introduces the risk of missed SLA windows and the chargeback exposure that follows. ## Related terms - EDI (electronic data interchange) - EDI 850 - EDI 856 - EDI 860 - EDI 997 - Purchase order ## Sources - X12 Transaction Sets - X12 Supply Chain Transaction Flow - X12 Examples: 855 Purchase Order Acknowledgment (004010X358) ## Frequently asked questions ### What is the difference between EDI 850 and EDI 855? The 850 is the buyer's purchase order. The 855 is the seller's acknowledgment of it, sent after the 850 is processed, affirming the order or indicating changes. ### What is the difference between EDI 855 and 856? The 855 belongs to the purchase order process and answers the order itself. The 856 Ship Notice/Manifest belongs to the delivery process and lists the contents of a shipment. ### What is the difference between EDI 855 and 997? A 997 reports the results of a syntax check on the documents received and does not cover the meaning of their data. The 855 is the seller's business answer to the order: what it accepts, changes or rejects. ### What is a 865 EDI document? The 865 is the X12 Purchase Order Change Acknowledgment/Request, Seller Initiated. The seller uses it to accept or reject a buyer's changes to an order, or to accept, reject or modify a purchase order.