<?php
	$conn = new mysqli('localhost', 'root', 'S1stemas', 'gascentro') or die(mysqli_error());	
	$id_departamento=intval($_REQUEST['client_id']);
	$municipios = $conn->prepare("SELECT * FROM plate WHERE person_id = '$id_departamento'") or die(mysqli_error());
		echo '<option value = "">--SELECCIONA--</option>';
	if($municipios->execute()){
		$a_result = $municipios->get_result();
	}
		while($row = $a_result->fetch_array()){
			echo '<option value = "'.$row['id'].'">'.utf8_encode( $row['code']).'</option>';
		}
?>