How To Fix /IWBEP/CM_MGW_RT181 - Is-Not-Modified is not allowed in case If-Modified-Since is initial

SAP Error Message - Details

• Message type: E = Error

• Message class: /IWBEP/CM_MGW_RT -

• Message number: 181

• Message text: Is-Not-Modified is not allowed in case If-Modified-Since is initial

Self-Explanatory Message

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Smart SAP Assistant

• What is the cause and solution for SAP error message /IWBEP/CM_MGW_RT181 - Is-Not-Modified is not allowed in case If-Modified-Since is initial ?

  The SAP error message /IWBEP/CM_MGW_RT181 with the description "Is-Not-Modified is not allowed in case If-Modified-Since is initial" typically occurs in the context of OData services when there is an issue with the handling of HTTP conditional requests. This error is related to the use of the If-Modified-Since HTTP header in requests to the OData service.
  Cause:
  The error arises when a client sends a request to the OData service with the If-Modified-Since header not set (i.e., it is empty or initial), but the server is trying to respond with a 304 Not Modified status. The 304 Not Modified response indicates that the resource has not changed since the specified date in the If-Modified-Since header. If this header is not provided, the server cannot determine whether to return a 304 response or the full resource representation.
  Solution:
  To resolve this error, you can take the following steps:
  
  
  Check Client Request: Ensure that the client making the request is correctly setting the If-Modified-Since header when it is expected. If the client does not need to use this header, it should not include it in the request.
  
  
  Modify Server Logic: If you have control over the OData service implementation, you may need to adjust the logic to handle cases where the If-Modified-Since header is not provided. This could involve:
  
  Returning the full resource representation instead of a 304 Not Modified response when the header is absent.
  Implementing a check to ensure that the Is-Not-Modified response is only sent when the If-Modified-Since header is present and valid.
  
  
  
  Review OData Service Configuration: Check the configuration of the OData service in SAP Gateway. Ensure that it is set up to handle conditional requests appropriately.
  
  
  Client-Side Handling: If you are developing the client application, ensure that it correctly handles the caching and conditional requests. It should only send the If-Modified-Since header when it has a valid timestamp to compare against.
  
  
  Related Information:
  
  OData Protocol: Understanding the OData protocol and how it handles caching and conditional requests can provide insights into why this error occurs.
  SAP Gateway Logs: Check the SAP Gateway logs for additional details about the request and response cycle, which may provide more context for the error.
  SAP Notes: Look for any relevant SAP Notes or documentation that may address this specific error or provide updates to the OData service framework.
  
  By following these steps, you should be able to resolve the error and ensure that your OData service handles requests correctly.