When upgrading from Strategy version 10.4 to Strategy version 2019 and configuring the Intelligence Server (I-Server) with Platform Analytics enabled, the following error message occurs when enabling the messaging service:
"Messaging Service for Platform Analytics is not a valid feature flag."
View the image below for reference:

The error message is appearing due to the fact that the Messaging Service for Platform Analytics is not a valid feature flag in older version of the metadata (MD).
This problem can be resolved after updating the metadata to corresponding version.
Follow these steps to update the metadata:
1. Configure the I-Server with "Send Intelligence Server telemetry to Platform Analytics" unchecked.
This is located in the Platform Analytics Configuration step. View the image below for reference:
2. Update your metadata using Configuration Wizard.
3. Re-configure and enable Platform Analytics.
For detailed guidance on how to update the metadata, please refer to detailed guidance in our Documentation.
Interested in learning more about Platform Analytics? Visit the Learning Center on Community!