EDI 855 (Purchase Order Acknowledgment)
EDI 855 is the ANSI X12 transaction set a supplier sends back to a buyer in response to an EDI 850 purchase order, confirming whether the order is accepted as sent, accepted with changes, or rejected. X12's own specification for the 850 explicitly excludes acknowledgment, so the 855 is the document that closes that loop, and many retailers enforce a strict deadline — often 24 to 48 hours — for sending one.
What EDI 855 does
When a buyer sends an EDI 850 purchase order, X12's own specification is explicit that the 850 is a one-way document — it isn't meant to convey a change or confirm receipt. The EDI 855 Purchase Order Acknowledgment is the transaction set that fills that gap: the supplier sends it back to say the order arrived, and to state what, if anything, is different from what was ordered.
An 855 can confirm an order exactly as submitted, confirm it with specific line-level changes (a lower available quantity, a different ship date, a substituted item), or reject it outright. Buyers use it to catch problems — a discontinued SKU, insufficient stock, a price that no longer matches the catalog — before the order gets as far as a shipment.
The BAK segment and acknowledgment codes
The header segment, BAK, carries the acknowledgment's core facts. BAK01 is a purpose code distinguishing an original acknowledgment from a change to one already sent. BAK02 is the acknowledgment type, and the codes that show up across most trading-partner guides are:
| Code | Meaning |
|---|---|
| AK | Accepted — no detail or change |
| AC | Accepted — with detail and change |
| AD | Accepted — with detail, no change |
| RJ | Rejected — no detail |
BAK04 carries the buyer's original PO date, and BAK08 carries the supplier's own order number for cross-reference. At the line-item level, the 855 has to return the original PO's line numbers unchanged, which is what lets the buyer's system reconcile a changed quantity or substituted item against the specific line it belongs to rather than guessing.
Why retailers enforce deadlines
Large retailers and distributors build EDI 855 compliance into their vendor scorecards: a supplier who doesn't acknowledge an order within a set window — one retailer's published guide requires it within one business day — risks a chargeback for the missed SLA, separate from any chargeback tied to the shipment itself.
The deadline exists because the acknowledgment is what lets the buyer act while there's still time: reorder from a backup supplier if an item is rejected, adjust a plan if a quantity drops, or flag a price discrepancy before the invoice arrives and the three-way match fails. An 855 that arrives after the shipment has already left has lost most of its value.
Where it sits in the order lifecycle
The 855 sits between the order and the shipment: EDI 850 (purchase order) → EDI 855 (acknowledgment) → EDI 856 (advance ship notice) → EDI 810 (invoice) → EDI 997 (functional acknowledgment of each of the above). Not every trading relationship requires all five — smaller suppliers sometimes skip the 855 entirely — but where it's required, it's the first checkpoint in the chain, and it's built on X12 version 4010 in most published retailer guides still in use.
Frequently asked questions
Is EDI 855 required for every purchase order?
No. It's required where the buyer's trading-partner specification or vendor agreement mandates it, which is common among large retailers and distributors but not universal. Where it's required, it's usually tied to a vendor scorecard and a response-time deadline.
What do the AK, AC, AD, and RJ codes mean on an 855?
AK means the order is accepted exactly as sent, with no changes. AC means accepted but with changes to line-level detail. AD means accepted with detail provided but no actual change. RJ means the order is rejected outright, with no further detail. The code lives in the BAK02 element of the header segment.
What happens if a supplier never sends an EDI 855?
The buyer has no electronic confirmation the order was received or will be fulfilled as submitted. Where an 855 is contractually required, a missing one typically triggers a compliance chargeback independent of whatever happens with the shipment itself.
How is EDI 855 different from EDI 856?
EDI 855 acknowledges the order before anything ships — it's a response to the purchase order. EDI 856, the advance ship notice, comes later and describes a shipment that's already on its way: what's packed, how, and on which carrier.