Recently while doing Dynamics 365 Portal deployment, got following dependency error regarding Web Notifications.

Checking target organisation I found web notification solution is already installed there. While troubleshooting, I found a helpful thread and Adxstudio Portal KB. We don’t need to use web notification now for Dynamics 365 portal, this solution is kept for the compatibility of the Adxstudio Portal solution. After removing reference for the web notification from workflows, solution imported successfully.

Hope it will help someone !!