Send JSON data from POST request to txt file

register.php

<?php
header("Content-Type: application/json; charset=UTF-8");
$data = json_decode(file_get_contents('php://input'), true);
//print_r($data);
foreach($data as $key => $value)
{
    $str.=$key.":".$value."\n";
}
$file = 'people.txt';
// Open the file to get existing content
$current = file_get_contents($file);
// Append a new person to the file
$current .= "new Record: \n".$str;
// Write the contents back to the file
file_put_contents($file, $current);
echo $str;
?>