Here is the control flow along with the variables pane.
The icons on the workflow indicate we have expressions thereon. The expression on the workflow constraint between tasks 1 and 2 is shown here. As you can see we want the workflow to be followed if our variable has a value of 0 and no errors occured on task 1.
Between task 1 and task 3 we also have an expression on the workflow and it looks like this
So the opposite in terms of the expression to the previous requirements. This time this route will only be followed if the task 1 succeeds and the variable value is NOT = 0. Between tasks 2 and 4 and 3 and 4 you can see a spotted line for the precedence constraint. This indictes a Logical OR (Either of the tasks (2 or 3) can trigger task 4).
So let's test the flow then. Note the changes in variable value
Variable value = 0
Variable value not = 0
