Custom Error message from Remote Event Receiver is not displayed in Modern UI

Question

When publishing a document in a SharePoint library we have a Remote Event Receiver checking various properties which may fail the publishing of the document. The Remote event receiver will return an error message which explains the reason for cancelling the publication.

It seems that Modern UI uses asynchronous calls to the SharePoint REST interface hitting the endpoint Publish() which in fact responds with an error (statuscode 500) and the correct error message.

{
"error": {

    "code": "-2130575223, Microsoft.SharePoint.SPException",

    "message": {

        "lang": "da-DK",

        "value": "PDF/HTML document(s) out of sync when publishing master document pinfoOUH-505196526-142. ServerRelativeUrl: /sites/pinfo-doc-OUH/Direktionssekretariatet/Kohsel/2024-11-13/05-01-2023_L\u00e6rCrawl.docx"

    }

  }
}

However as can be seen from the screendump below the only message being displayed to the user is "Mislykkedes", which means "failed" in danish.

Is this by design or is it a bug?

Our environment is SharePoint server 2019. Build 16.0.10404.20003

User's image

Answer

Hello,

I can try to help.

Modern UI Behavior:

Modern UI in SharePoint uses asynchronous REST calls, which may not process or display the full custom error message returned from the backend.
This behavior might be by design, as the Modern UI often simplifies error messages for end users.

Localization or Fallback Mechanism:

The system may default to a localized generic error message ("Mislykkedes") instead of the specific error details.

Error Handling Differences:

The Modern UI might suppress or ignore detailed error messages for security or usability reasons, which could lead to the generic error being displayed instead of the full custom message.

Best Regards,

Ali Koc

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Custom Error message from Remote Event Receiver is not displayed in Modern UI

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