Recently while trying to come to a solution on writing custom scripts on Flow designer I came to knowing exactly what needs to be done to include a script inside a Flow. This might or might not be a problem that you need to solve , especially when there are so many OOB Actions .

But it all comes to writing efficient code , when you know in and out Scripting in ServiceNow at a platform level .

So here it is mentioned in Steps :-

1. Create an Action
2. Define the Inputs .
3. Add a Script Step in Between .
4. Define the Outputs .

And wala , you have played your part and created a custom Action Script to be included as a part of your Flow .The Screenshots would help in the same !!