Creating ByteArray in Kotlin

as an option you can create simple function

fun byteArrayOfInts(vararg ints: Int) = ByteArray(ints.size) { pos -> ints[pos].toByte() }

and use it

val arr = byteArrayOfInts(0xA1, 0x2E, 0x38, 0xD4, 0x89, 0xC3)