How to append data in child table through api

I am trying to add a new value to this child table but it updates the existing value, I want a new row how to achive it?
url: “/api/resource/In Out”,
dataType: ‘text’,
type: ‘POST’,
contentType: ‘application/json’,
data: JSON.stringify({
parent: att,
parenttype: ‘Attendance’,
punch_in_out: ‘Punch In’,
punch_time: ‘12:06:00’
beforeSend: function (xhr) {
xhr.setRequestHeader(‘X-Frappe-CSRF-Token’, frappe.csrf_token);
success: function (data) {
error: function (error) {
var string = error.responseText;
var json_object = JSON.parse(string);
var msg_object = JSON.parse(json_object._server_messages);
var msg = JSON.parse(msg_object[0]);