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Hello @rosario.guaia
Based on the tutorial, the Streaming Data is included with Eikon Data API version 1.1.2. Which version of Eikon Data API that you are using? You can use 'pip show eikon' or 'pip list' command to check the version of Eikon Data API in your environment.
If you Eikon Data API is outdated, you can follow the steps in How to update your Eikon Data API page to update your Eikon library.