Transaction set guide

EDI 850 Purchase Order

The 850 is the most common X12 transaction. The retailer (buyer) sends it to the supplier (seller). It says: "Here is what I want, in what quantity, where to ship it, and when I want it."

The 850 envelope hierarchy

1. ISA — interchange envelope.
2. GS — function group, qualifier PO for purchase orders.
3. ST — transaction set, ID 850.
4. BEG — beginning of purchase order. Required.
5. REF loop — references (vendor, customer, contract).
6. DTM loop — dates (ship-by, deliver-by, cancel-after).
7. N1 loop — names and addresses (ship-to, bill-to).
8. PO1 loop — line items (one PO1 per item).
9. CTT — line item total count.
10. SE / GE / IEA — trailers.

Required segments (X12 baseline)

Segment	Purpose	Required by X12?	Often required by partners?
BEG	PO type, purpose, PO number, date	Yes	Yes
REF	Vendor / contract / department references	No	Often (REF*VR, REF*DP)
DTM	Dates (ship-by, deliver-by, cancel)	No	Often (DTM*002, DTM*010)
N1 / N3 / N4	Ship-to address	No (loop)	Almost always (N1*ST)
PO1	Line item	Yes	Yes
PID	Item description	No	Often
CTT	Total line count	Yes	Yes
SE	Transaction trailer	Yes	Yes

BEG segment — the PO header

BEG*00*SA*PO12345**20250506~

• BEG01 — transaction set purpose code. 00 = original, 01 = cancellation, 04 = change.
• BEG02 — purchase order type. SA = stand-alone, BC = blanket, RL = release.
• BEG03 — purchase order number. The retailer's PO number — case-sensitive, must match exactly when you reference it later.
• BEG05 — PO date in YYYYMMDD.

PO1 segment — line items

PO1*1*5*EA*12.50**VC*ABC123*UP*012345678905~

• PO1-01 — line number.
• PO1-02 — quantity.
• PO1-03 — unit of measure (EA = each, CA = case, LB = pound).
• PO1-04 — unit price.
• PO1-06 / PO1-07 — first product ID qualifier + value (VC = vendor catalog, BP = buyer's part, UP = UPC).
• PO1-08 / PO1-09 — second product ID qualifier + value.

The five most common 850 rejections

1. Missing REF*VR (vendor number). Most large retailers require their vendor number on every PO.
2. Wrong N1 qualifier. N1*ST = ship-to, N1*BT = bill-to, N1*BY = buyer. Mixing them up rejects.
3. UPC mismatch. Retailer expects UP qualifier; you sent VC. Or the UPC checksum is wrong.
4. CTT line count off-by-one. CTT must equal the count of PO1 segments, not the SE segment count.
5. SE segment count wrong. SE-01 must equal the number of segments from ST to SE inclusive.

How to validate an 850 in EDI-X12

1. Open the validator.
2. Paste your 850, or click Load sample 850.
3. Click Validate. Window 2 shows structural issues.
4. Click Explain with AI. Window 3 walks through every segment.

Related

• 856 ASN — the response to your 850
• 810 Invoice — billing back the PO
• 997 — confirming you received the 850
• Glossary of qualifier codes