I believe that Autodesk have discounted the Structural Analysis for Revit service, so the link has been removed. Please see below link
https://structuralanalysis.360.autodesk.com/
You still have the app to link it directly into Robot Structural Analysis Pro
Structural Analysis Toolkit 2019
I hope this answers your question.
Thanks
Gareth
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Twitter: @TheDarkAsset
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Gareth Spencer
BIM Technical Consultant | Man and Machine (UK)