You have to call your secondary constructor, which expects a trailing name parameter:

    val person1 = Person("Joe", 25, "name") //prints Age = 25
    val person2 = Person("Joe", 25) //prints nothing

In your example, the primary constructor gets chosen as your argument list maps its parameters.

in your code val person1 = Person("Joe", 25) your are calling a constructor wich have two parameters and thats the first constructor not the second.
call the second constructor like that val person1 = Person("Joe", 25,"name").
i hope that was clear.

I am learning kotlin and I was reading about constructors: primary and secondary.

Here is my question that how should I access primary constructor parameters inside a secondary constructor. I am unable to access but I am not sure why? Why I am not able to access it directly?
If anyone knows please help me understand this concept in a better way. Why I am not able to access it?

I have created one demo class with two constructors here is my code:

fun main(args: Array<String>) {

    val person1 = Person("Joe", 25)
    println("First Name = ${person1.firstName}") // working, printing first name 

}

class Person(val firstName: String, var age: Int) {

    constructor(sectionName: String, id: Int, name: String) : this(sectionName,id)  {
        println("Age = ${age}") // not working, no output
    }

}

Or Am I doing anything wrong?

PS: I know I can write init block and assign the parameters to the class variable and it is working as expected.