You've attached the wrong application (despite the name of the attached Tutorial 5-6.tersus, the project actually matches Tutorial 4-5).
In general a flow whose color is red rather than black, is an indication of an invalid flow, caused by one of several reasons. such as a missing source or target, or a different data types at each end of the flow. To find out the reason in your specific case, use the Validation view, which displays all identified issues in your model, not just invalid flows (the view is first mentioned in page 14).
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