How To Fix WS635 - External reference number &1 was exchanged for document &2

SAP Error Message - Details

• Message type: E = Error

• Message class: WS - Supplier Billing Document

• Message number: 635

• Message text: External reference number &1 was exchanged for document &2

What causes this issue?

The number of read accesses in the program is restricted to &V1&.

System Response

The system outputs the hits in a sorted sequence, however since the
maximum number of hits has been restricted the list might not match the
database in the sorted area.

How to fix this error?

You can set a temporary restriction either by using a report variant or
on the selection screens themselves.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.

Smart SAP Assistant

• What is the cause and solution for SAP error message WS635 - External reference number &1 was exchanged for document &2 ?

  Certainly! Here's a detailed explanation for the SAP error message:
  
  SAP Message:
  WS635 - External reference number &1 was exchanged for document &2
  
  Meaning / Cause:
  This message occurs when you try to post or process a document with an external reference number that has already been used in another document. SAP enforces uniqueness for external reference numbers in certain document types (e.g., accounting documents, invoices, or payment documents) to avoid duplication and ensure data integrity.
  
  &1 = The external reference number you tried to use.
  &2 = The document number that already contains this external reference number.
  
  In other words, the external reference number you are trying to assign has already been assigned to another document, so SAP "exchanges" or replaces it with the existing document number to prevent duplication.
  
  Typical Scenarios:
  
  Posting an invoice or payment with an external reference number that is already assigned to another document.
  Incoming payment processing where the external reference (e.g., check number, invoice number) is duplicated.
  Document clearing or reconciliation where external references must be unique.
  
  
  Solution / How to Resolve:
  
  
  Check the existing document:
  
  Use the document number (&2) provided in the message to review the existing document that already contains the external reference number.
  Transaction codes like FB03 (Display Document) or FBL1N/FBL5N (Vendor/Customer Line Items) can be used to check the document details.
  
  
  
  Verify the external reference number:
  
  Confirm if the external reference number you are trying to use is correct or if it was mistakenly reused.
  If the external reference number is incorrect, correct it before posting.
  
  
  
  Adjust the external reference number:
  
  If the external reference number must be unique, assign a different external reference number to the new document.
  Coordinate with the business or accounting team to ensure the correct reference number is used.
  
  
  
  Check configuration (if applicable):
  
  In some cases, the uniqueness check for external reference numbers can be controlled via configuration or customizing settings.
  For example, in Financial Accounting (FI), the field "External Reference" (XBLNR) uniqueness can be enforced or relaxed depending on the business process.
  Consult with your SAP FI consultant or check customizing under Financial Accounting > Document > Document Header > Define Document Types or related settings.
  
  
  
  If duplicate external references are allowed:
  
  If your business process allows duplicate external references, check if any user-exit or BAdI is enforcing uniqueness and adjust accordingly.
  However, this is generally not recommended as it can cause reconciliation issues.
  
  
  
  
  Additional Information:
  
  The external reference number is often used to link SAP documents to external documents such as invoices, purchase orders, or payment references.
  Ensuring uniqueness helps in audit trails and prevents posting errors.
  This message is informational but indicates a potential data conflict that should be resolved.
  
  
  Summary:
  
  
  
  Aspect
  Details
  
  
  
  
  Message Number
  WS635
  
  
  Cause
  External reference number already exists in another document.
  
  
  Effect
  SAP prevents duplication by exchanging the external reference number with existing doc.
  
  
  Solution
  Check existing document, verify and correct external reference number, or assign a new one.
  
  
  Transactions to check
  FB03, FBL1N, FBL5N
  
  
  Configuration area
  Financial Accounting document types and reference number settings
  
  
  
  
  If you need help with a specific transaction or scenario where this message appears, please provide more details!