POSTMAN - How to use random number in the request

Just use the variable randomInt, for example:

In the request:
{
    "id": "{{$randomInt}}"
}

In the pre-request Script:

postman.setEnvironmentVariable("myId", "MY_ID_"+ _.random(1,99999));
console.log(postman.getEnvironmentVariable("myId"));

Read this link for more information: https://learning.postman.com/docs/postman/variables-and-environments/variables/