3800317 - WDA: "400 session not found" message appears when a external URL is called from an embedded Web Dynpro ABAP application within SAP GUI

• A secondary action inside a Web Dynpro ABAP (WDA) application — such as a download, export, or file generation button — is clicked while the application is running in the SAP GUI embedded browser (SAP GUI for Windows with Webview2 / Edge control).
• The OS default browser (e.g., Microsoft Edge) opens automatically.
• The external browser immediately displays:"400 Session not found".
•  No logon prompt is shown before the error appears.
• The issue occurs every time the action is triggered.
• The Web Dynpro application itself loads and operates correctly within the SAP GUI embedded browser — only the action that opens the external browser fails.
•  Workaround observed: opening the same URL directly in the external browser, authenticating manually, and refreshing the failed browser tab resolves the display temporarily.

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