If you have a kind of session ID or something that you are passing in your payload in your request on postman and you want it to be generated randomly with each call, use the randomAlphaNumberic function as follows:

{
  "details": "show me the stuff",
  "session_id": "{{$randomAlphaNumeric.substr(0,5)}}"
}

In the above example, Postman generates a random 5 char alphanumeric in every request.

That’s it, Enjoy!