Troubleshooting Edi 855 Acknowledgment Issues

What This Is

This guide provides a comprehensive, practical reference for troubleshooting EDI 855 Purchase Order Acknowledgment issues encountered during EDI trading partner exchanges. An EDI 855 is used to confirm receipt of a purchase order and to communicate acceptance, rejection, or changes to items or quantities. Problems with 855 transactions cause order processing delays and can trigger chargebacks from retailers due to ASN/PO mismatches and OTIF non-compliance.

The guide explains why typical 855 failures occur, shows real EDI snippets annotated line-by-line, demonstrates how to convert 855 data into CSV for downstream systems, and offers step-by-step remediation actions. It emphasizes validation steps that PlainEDI provides and links to related resources for deeper topics such as delimiter issues, 997 acknowledgments, and PO/ASN management.

Who This Is For

This guide is intended for EDI analysts, integration engineers, warehouse managers, 3PLs, and small-business vendors who process EDI Purchase Order Acknowledgments (855) and must resolve errors quickly to maintain retailer compliance and uninterrupted fulfillment.

Key Segments Explained

Understanding the role of each major segment in an 855 is essential to troubleshooting. Below are the key segments you will encounter and what validation checks to run on each.

ISA/IEA — Interchange Control Header and Trailer

ISA establishes the interchange envelope and contains fixed-length elements that define sender/receiver IDs, date/time, and delimiters. IEA closes the interchange and carries the interchange control number. Common failures: mismatched ISA13/IEA02 control numbers, incorrect delimiter characters in ISA (ISA16 contains component element separator). Validate that ISA control numbers increment and match the IEA control count.

GS/GE — Functional Group Header and Trailer

GS defines functional group ID (e.g., PO for purchase orders) and carries a group control number. GE closes the group and must match the GS control number. Errors occur when batching changes control numbers or when different trading partners expect single or multiple transaction sets per group. Ensure GS/GE counts and control numbers align.

ST/SE — Transaction Set Header and Trailer

ST starts the 855 transaction set and contains the transaction set control number. SE ends the transaction set and must include the same transaction set control number and an accurate segment count. Most trading partner rejections are due to ST/SE control number mismatches or incorrect SE segment counts. Always recalc segment count after programmatic segment insertion or removal.

BAK — Beginning Segment for Purchase Order Acknowledgment

BAK carries the acknowledgment type code (e.g., AK=Acknowledgment, NE=Not Accepted) and the original PO number with date. Common problems: wrong BAK02 (PO number) format, missing PO date, or mismatched PO number compared to the original 850. Validate exact matching of PO numbers and formatting conventions required by the partner (leading zeros, suffixes).

PO1 — Baseline Item Data

PO1 lines convey item-level acknowledgments: quantity ordered vs. acknowledged, unit of measure, and item identifiers (UPC/SKU). Key sub-elements: PO101 (line item identifier), PO102 (quantity ordered), PO103 (unit of measure), PO104-PO106 (unit price/qualifiers). You must ensure PO1 line sequence numbers and referenced PO line numbers match the original 850.

CTT — Transaction Totals

CTT carries the number of line items; trading partners validate the CTT count versus number of PO1 segments. A mismatch triggers rejection or manual review. Always update CTT when adding or removing PO1 segments during processing.

Example EDI Snippet

The following is a realistic EDI 855 example. The code is followed by line-by-line annotations explaining why each segment matters for troubleshooting.

ISA*00*          *00*          *ZZ*SENDERID      *ZZ*RECEIVERID    *210101*1253*U*00401*000000905*0*T*:~
GS*PR*SENDERID*RECEIVERID*20210101*1253*905*X*004010~
ST*855*0001~
BAK*00*AC*PO1234567*20210101~
REF*IA*PO1234567~
N1*ST*Company Name*92*12345~
PO1*1*10*EA*12.34**VP*123456789012~
PO1*2*5*EA*3.21**VP*987654321098~
CTT*2~
SE*10*0001~
GE*1*905~
IEA*1*000000905~

Annotations:

• ISA: Check ISA13 (000000905) equals IEA02. ISA contains delimiters: note the last character : is component separator per ISA16. If a trading partner expects a different component separator, parsing will fail.

• GS: GS06 (905) must match GE02. Group control number mismatches cause partner rejection.

• ST/SE: ST control number 0001 must equal SE02. SE01 must contain correct segment count: in this example SE*10 (there are 10 segments in the ST-SE block). Recalculate when adding extra REF or N1 segments.

• BAK: BAK03 is the PO number; it must exactly match the 850 PO number. BAK01 code 00 indicates original; BAK02 AC indicates accepted change acknowledgment—validate partner-specific codes.

• PO1: Each PO1 contains the line item quantity acknowledged as the second element (10 and 5) and the VP qualifier for vendor part number mapping. Validate that PO1 sequence numbers (first element) reflect the PO line numbers from the 850 or are formatted per partner rules.

• CTT: CTT*2 indicates two line items. If the system inserted an extra PO1 for a canceled line but failed to increment CTT, the trading partner rejects the file.

CSV Output Example

Converting 855 data into CSV simplifies ingestion into ERPs. Below is a sample CSV mapping for the EDI snippet above. The CSV columns include PO number, PO date, line number, sku, ack_quantity, unit_price, acknowledgment_code, and ship_to.

Step-by-Step Conversion Process

Follow these steps to convert an incoming 855 into a validated CSV and resolve common acknowledgment issues programmatically.

1. Receive and Validate Interchange Envelope

   1. Verify ISA/IEA control numbers match and that the ISA delimiters are the expected characters. If delimiters differ, adjust parser settings or reject the interchange with an explanatory 997.

   2. Validate GS/GE group counts and that GS06 equals GE02.

2. Validate Transaction Set Structure

   1. Confirm ST/SE control numbers match. Recompute SE segment count by counting segments between ST and SE inclusive. If SE count is incorrect, update SE and regenerate the 997 response to inform the partner.

   2. Run schema validation against the 855 transaction set to detect missing required segments like BAK or PO1.

3. Cross-Reference with the Original 850

   1. Lookup the original PO (PO1234567) in your order management system. Compare PO numbers, dates, and PO1 line identifiers. If BAK03 deviates from the stored PO number, flag for manual review and notify the partner.

   2. For each PO1, ensure PO1 line quantity does not exceed the original ordered quantity unless a change order exists. If quantities change, ensure acknowledgment codes in BAK or specific PO1-level codes indicate acceptance with change.

4. Parse Item-Level Acknowledgment and Map to CSV

   1. Extract PO1 elements: line number, quantity, unit, price, product ID qualifiers and values. Normalize SKU to your internal format using qualifiers (e.g., VP, UP).

   2. Create CSV rows per PO1, ensure CTT count equals number of CSV rows, and include BAK-level acknowledgment code in each row if no line-level ack exists.

5. Run Business Rules and Compliance Checks

   1. Enforce partner-specific PO number formatting, ship-to location IDs, and unit of measure conversions. For example, convert “EA” to your ERP’s internal UOM if needed.

   2. Check for promised ship dates (DTM segments) and ensure they fall within acceptable lead times. If a date violates SLA, raise an exception and notify the buyer.

6. Generate 997 Functional Acknowledgment and Error Responses

   1. Send a 997 acknowledging receipt of the 855, and include AK2/AK5 codes that reflect acceptance or specific rejection reasons. Use the partner’s required codes and include AK4 element positions for segment-specific errors.

   2. When PlainEDI validation prevents the error, the 997 generation is automated to show accepted vs. rejected segments.

7. Deliver CSV to ERP and Log the Exchange

   1. Deliver the CSV file to the ERP and capture transaction IDs, control numbers, and any manual overrides for audit trails.

   2. Archive the original EDI interchange for dispute resolution and compliance reporting.

Common Errors and Fixes

Below are frequent 855 errors, common partner error notations where applicable, and practical fixes. Include these checks in automated validation pipelines such as PlainEDI to prevent rejections.

• Error: ST/SE control number mismatch or SE segment count wrong. Fix: Recompute the exact number of segments between ST and SE inclusive; ensure SE02 matches ST02. If you already transmitted, resend corrected 855 and generate a 997 with AK5 code 5 (rejected) and AK4 detail for the SE count position.

• Error: ISA13/IEA02 or GS06/GE02 control numbers mismatch. Fix: Align interchange/group control numbers during batching. Increment the control numbers consistently across ISA/GS and corresponding trailers. Prevent programmatic resets at system restarts by persisting control counters.

• Error: BAK03 (PO number) does not match original 850 PO number. Fix: Verify PO normalization rules (leading zeros, prefixes). If formatting differs, transform the incoming PO number to the partner’s canonical form. If the number is truly incorrect, reject and request corrected 855.

• Error: PO1 quantity discrepancy without an accompanying change code. Fix: Ensure that when acknowledging different quantities you include a proper acknowledgment type (BAK02) and line-level status/quantity change segments as required by the partner. Log reason codes for partial ship or backorder and include dates in DTM segments.

• Error: Delimiter or component element separator mismatch detected in ISA. Fix: Check ISA16 and ISA11 for repetition separator and component element separator definitions used by the partner. Configure your parser to use the specified characters. Use PlainEDI’s delimiter detection to validate incoming files before parsing.

• Error: Missing required N1 ship-to or REF location IDs. Fix: Validate that required N1/N3/N4 loops are present and that the N101 qualifier (e.g., ST or BT) is correct. For missing IDs, query the trading partner or fall back to the default ship-to configured for the PO. Document exceptions in the transaction log.

• Error: CTT line count mismatch. Fix: Recount PO1 segments and update the CTT element accordingly. If your system filters or expands lines during processing, include those adjustments in the CTT calculation.

Related Resources

Use these internal guides to deepen your knowledge and link troubleshooting steps with other EDI topics:

• understanding EDI X12 delimiters and structure
• reading 997 functional acknowledgments
• common EDI 850 validation errors and fixes
• how to validate EDI files before sending
• integrating EDI with ERP systems
• edi-to-csv for small business vendors
• reading lowes edi files

FAQ Section

Q: What causes an 855 to be rejected by a trading partner?

Rejects occur due to structural errors (ST/SE control mismatch, wrong segment counts), envelope issues (ISA/IEA or GS/GE mismatches), missing required segments (BAK, PO1, CTT), data mismatches against the original 850 (PO numbers, line items, quantities), or delimiter misconfiguration. Partners also reject when required partner-specific qualifiers are missing. Use automated validation to catch these before transmission.

Q: How do I correct an incorrect SE segment count?

Recalculate the segment count between ST and SE inclusive. Update SE01 with the correct count and ensure SE02 equals the ST control number. Resend the corrected transaction and send a 997 indicating the original was rejected if applicable. Persist segment count logic so programmatic changes to the transaction are always reflected in SE.

Q: What should I include in a 997 when informing a partner of a rejection?

Include AK1 identifying the functional group, AK2 referencing the transaction set (ST02), AK5 with the acceptance/rejection code, and AK4 details to identify the exact segment and element positions that failed. Use precise AK4 position numbers and reject codes mapped to your parsing and schema validation steps.

Q: Why are control numbers out of sync after a system restart?

Control counters stored in volatile application memory reset after a restart. Persist ISA/GS/ST control counters to durable storage or a database. Implement a check that compares outgoing control numbers against expected values and halts transmission if anomalies exist.

Q: How do I handle line-level partial acceptance in an 855?

Use proper line-level acknowledgment codes and include quantities reflecting acceptance or backorder. Populate line-level status or DTM segments with expected ship dates for backordered quantities. Ensure that BAK02 and any partner-required segments denote a change acknowledgment if quantities differ from the 850.

Q: Can delimiter differences break EDI parsing?

Yes. The ISA segment defines element, component, and segment terminators. If your parser uses different delimiters than specified by ISA, elements will not parse correctly and will result in structural errors. Detect and configure delimiter characters per interchange using ISA11 and ISA16 before parsing.

Q: What are the best practices to avoid 855 errors?

Persist control numbers, perform pre-transmission validation of ISA/GS/ST envelopes and segment counts, cross-validate BAK PO numbers against your internal PO store, enforce PO1 sequence and quantity checks, and run partner-specific compliance rules. Use PlainEDI to catch delimiter and envelope issues and to automate 997 generation.

Q: How does PlainEDI help prevent 855 issues?

PlainEDI provides automated validation that checks ISA/GS/ST envelopes, delimiter configuration, required segment presence, segment counts, and partner-specific rules before transmission. PlainEDI surfaces errors with actionable messages and can regenerate corrected transactions. Use PlainEDI to upload test files for validation and to automate 997 responses.

Case Studies and Real-World Examples

Case Study 1 — Retailer PO Number Format:

A vendor repeatedly received 855 rejections because their system stripped the leading zeros from PO numbers. The vendor normalized PO numbers by storing original PO with leading zeros and implementing a transformation rule during both inbound parsing and outbound acknowledgment generation. They also added a validation rule in PlainEDI to reject any 855 where BAK03 does not match the canonical PO format.

Case Study 2 — SE Segment Count After Adding Notes:

A 3PL inserted free-form REF segments containing internal comments into the 855 after automated generation. The additional segments caused SE count mismatches. The 3PL updated their pipeline to recalculate segment counts after any insertion and to run a pre-send schema check. They then used PlainEDI’s preflight validator to ensure control numbers and counts matched before exchanging with the retailer.

Case Study 3 — Partial Acceptance Handling:

A vendor reduced quantities for some lines and did not include DTM promised dates for the backordered items. The retailer flagged the transaction for manual review and applied chargebacks. The vendor updated PO1 handling to include line-level reason codes and DTM segments with promised ship dates and used partner-specific codes required by the retailer. This eliminated manual reviews for similar future changes.

Troubleshooting Checklist (Quick)

• Verify ISA/IEA and GS/GE control numbers.

• Recompute ST/SE segment counts and matching control numbers.

• Confirm BAK03 matches the original 850 PO number exactly.

• Validate PO1 quantities against original PO; include change codes for differences.

• Ensure CTT lines count equals actual PO1 segments.

• Check delimiter settings in ISA and configure parser accordingly.

• Run partner-specific compliance rules and generate a 997 with AK2/AK5/AK4 details on errors.

When you want to validate 855 files quickly, upload sample files to PlainEDI for automated parsing and detailed error messages. PlainEDI’s validator prevents the most common 855 issues and generates 997 reports that pinpoint segment- and element-level failures.

To convert validated EDI 855 files into CSV for your ERP, export the parsed data following the CSV mapping above and deliver via SFTP or direct integration. If you need assistance building mapping templates or automating these flows, integrate with your ERP using the techniques outlined in the integrating EDI with ERP systems guide.

Ready to validate or troubleshoot an 855 now? Upload your file to PlainEDI to run the detailed checks and receive a parsed CSV output and a 997-ready error report.