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,