Interactions in flows are no longer supported by the Run Interaction shape
Valid from Pega Version 7.3.1
The Run Interaction shape in flows has been replaced by the Run Data Flow shape, which supports running a single case data flow with a strategy. Flows that include the Run Interaction shape continue to work; however, you must now use the Utility shape to reference any new interactions that you create.
For more information, see Running a decision strategy from a flow and About Interaction rules.