The data sources have been added, but the data sources need to be connected to the endpoint to send responses. The completed pipeline should look like the following.
Drag a line from the findVariantById unit to the Endpoint unit to connect the two units.
Drag a line from the findEngineById unit to the Endpoint unit to connect the two units.
Do the same for the findModelById unit.
The Request unit is connected to the data source units, which are themselves connected to the Endpoint unit.
To continue, see Map attributes to parameters.