Why value is not updated in JSON using PHP and jQuery?

I stuck at the JSON file whereby the value is not updated.

Reference:

1. How to update/edit a JSON file using PHP [closed]
2. Add, Update, Delete and Read JSON Data/File in PHP
3. Modifying a JSON file with PHP

JSON (../assets/data/maintenance.json)

[
    {
        "maintenance_status":"off"
    }
]

PHP (file_update.php)

<?php
$data = file_get_contents('../assets/data/maintenance.json');  // able to read file
$json_arr = json_decode($data, true);

$newValue = $_POST['newValue'];
foreach ($json_arr as $key => $value) {
    $json_arr[$key]['maintenance_status'] = $newValue;
}

file_put_contents('../assets/data/maintenance.json', json_encode($json_arr));
echo json_encode($json_arr); // return [{"maintenance_status":"on"}] at jQuery success response
?>

jQuery

$('.maintenance-toggle').on('click', function(){
    $('.maintenance-toggle').toggleClass('on');
    if ($('.maintenance-toggle').hasClass('on')){
        updateValue("on");
    }
    else if ($('.maintenance-toggle').hasClass('off')){
        updateValue("off");
    }
});

function updateValue(newValue) {
    console.log(newValue); // received "on" or "off"
    $.ajax({
        url : '../src/files/file_update.php',
        type : 'POST',
        data: { 
            newValue: newValue
        },
        cache: false,
        success: function(response){
            console.log(response); // success since received result from echo php but not update the value in JSON
        },
        error: function(e){
            
        }
    });
}