Fetch data with getJSONArray in kotlin - json

Question

I'm trying to fetch some data from json. I made function to fetch JSON.
My code:
val obj = JSONObject(getJSONFromAssets()!!)
val userArray = obj.getJSONObject("user_id")
My code to fetchAssets:
private fun getJSONFromAssets(): String ?{
var json: String? = null
val charset: Charset = Charsets.UTF_8
try{
val jsonFile = assets.open(K.json.jsonFileName)
val size = jsonFile.available()
val buffer = ByteArray(size)
jsonFile.read(buffer)
jsonFile.close()
json = String(buffer, charset)
}
catch (ex: IOException){
ex.printStackTrace()
return null
}
return json
}
JSON File:
{
"user_id": "1",
"acounts": [
{
"id": "1",
"AccountNumber": "HR123456789012345678901",
"amount": "2.523,00",
"currency": "USD",
"transactions":
UserModelClass:
data class UserModelClass (
val user_id:String,
val accounts: List<AccountsList>
)
Problem is that I have user ID and then accounts where I can loop easy.
Error: Failed to open file, no such file or directory.
Value 1 at user_id of type java.lang.String cannot be converted to JSONObject