Error "Data Sources That Contain Logical Tables Cannot Be Used As Secondary Data Sources For Data Blending"

Option 1: Include all linking fields in the view, and aggregate secondary fields

Data blending will work when the secondary data source uses logical tables, as long as the following conditions are met:

1. All active linking fields from the primary data source must be included in the view on a shelf other than the Filters shelf
2. All fields from the secondary data source are aggregated, including dimensions

Option 2: Rebuild view with the data source using logical tables as the primary data source

The primary data source is set when the first field is dragged into the view. Once the primary data source is set, there is no way to change it; The view must be rebuilt from scratch
 

Option 3: Use joins instead of blending

Instead of blending multiple data sources, create one data source that joins all of the data using either physical or logical joins. If one or more of the data sources is a published data source, then the data cannot be joined in Tableau Desktop, but can be joined in Tableau Prep.
 

Option 4: Rebuild the data source using only physical joins 

1. Drag the first table to the relationship canvas.
2. Double-click on the logical table in the canvas. This will open the physical layer.
3. Drag additional tables to the join canvas to combine them using joins or unions.

Option 5: Need to load the 2 datasources separately

 https://jimdehner.com/bgs-beyond-getting-started-the-path-to-understanding-tableau/ the 3rd session where its is explains the connections to load the 2 sources separately.

Reference Community article.

The article The Tableau Data Model provides detailed information about Logical and Physical layers.