The scope prefix "$WORKFLOW:" cannot be used in an InlineScript activity. To reference a workflow variable in an InlineScript ...

The scope prefix "$WORKFLOW:" cannot be used in an InlineScript activity. To reference a workflow variable in an InlineScript activity, use the prefix "$USING:" instead. Workflow variables cannot be modified from an InlineScript activity. To change a workflow variable, assign the output of the InlineScript activity to that variable.