Got it, you need to be on PAD version with the new error warning (It ws 2.27 or 2.28), then:
- create new subflow, let's name is "subflow"
- then in main add action run subflow and select your subflow - that's the window
And now - if you make some errors in the logic usign your subflow, it will show the error
You can for example make this recursion:
1. Create Subflow_1
2. Create Subflow_2
3. in Subflow_1 add action to run Subflow_2
4. in Subflow_2 add action to run Subflow_1