Field notes
Segment-level explanations of the transaction sets people actually get stuck on, written for whoever is holding a broken file at four in the afternoon. No gated PDFs, no newsletter wall.
A segment-by-segment walkthrough of a real ANSI X12 850 purchase order: ISA, GS, ST, BEG, N1 loops, PO1 line items and the CTT/SE trailers, in plain English.
What AK3, AK4, and AK5 error codes actually mean in an X12 997 functional acknowledgment, and how to trace a rejection back to the segment that caused it.
How an X12 810 invoice maps to a paper invoice: BIG header, N1 party loops, IT1 lines, TDS totals and the SAC allowance/charge segments behind most disputes.
Shipment, order, tare, pack and item levels in an X12 856 advance ship notice: why HL loops confuse everyone and how to read the parent-child structure.