Trying Insertion sort in Kotlin

Can someone please review my code, why its not working. The same code works fine in Javascript.

https://pl.kotl.in/HFn2eGQmO?theme=darcula

val A = mutableListOf(4,8,2,9,5) for (j in 1..A.count() - 1) { val key = A.get(j) var i = j-1 while(i >= 0 && A[i] > key) { A.set(i+1, key) println(A[i+1]) i = i - 1 } A.set(i+1, key) }