Getting designated id in tables in MYSQL UPDATE

Question

The problem here is I can't get a designated "id" when I tried to update a row table.

<?php
if(isset($_POST['btn-input'])){
	$username = $_POST['username'];
	$name = $_POST['farmername'];
	$numofchicks = $_POST['numofchicks'];
	$price = $_POST['price'];
	$weight = $_POST['weight'];
	$get_id = $_GET['get_id'];

  //Outgoing
	mysqli_query($dbconn, "INSERT INTO chickens_out(username, farmername, numofchicks, price, weight) VALUES('{$username}','{$name}', '{$numofchicks}', '{$price}', '{$weight}')");
	mysqli_query($dbconn, "UPDATE chickens_out SET price = price * $weight * $numofchicks WHERE id = '$get_id'");	
}

Answer 1

Why all have $_POST and it has $get_id = $_GET['get_id'];.

Should it be :

$get_id = $_POST['get_id'];