Cloud SQL and php Redirect not working together

[garagef...@gmail.com]

Hello. I'm new to coding. The php code generated by my offline software works well with the localhost and mysql. But once its linked to cloud sql of Google App Engine Standard Environment, the php form is not redirecting to the success page. Though with the cloud sql, form data is successfully submitted but then a blank screen appears with no change in url. While with localhost, the success page is appearing after the form gets submitted. To adapt the code for GAE cloud sql, I've inserted $mysql_port and $mysql_Socket variables manually, those are not there in the original code that worked on localhost.

The code is :-

<?php
if ($_SERVER['REQUEST_METHOD'] == 'POST' && isset($_POST['formid']) && $_POST['formid'] == 'My-Form-Name')
{
$success_url = './success-page.html';
$error_url = './error-page.html';
$error = '';
$mysql_server = null;
$mysql_database = 'My-DB';
$mysql_table = 'My-Table';
$mysql_username = 'My-Username';
$mysql_password = 'My-Password';
$mysql_port = null;
$mysql_socket = '/cloudsql/CloudSql-Instance-Connection-Name';
$eol = "\n";
$db = mysqli_connect($mysql_server, $mysql_username, $mysql_password, $mysql_database, $mysql_port, $mysql_socket) or die('Failed to connect to database server!<br>'.mysqli_error($db));
mysqli_set_charset($db, 'utf8');
mysqli_query($db, "CREATE DATABASE IF NOT EXISTS $mysql_database");
mysqli_select_db($db, $mysql_database) or die('Failed to select database<br>'.mysqli_error($db));
mysqli_query($db, "CREATE TABLE IF NOT EXISTS $mysql_table (ID int(9) NOT NULL auto_increment, `DATESTAMP` DATE, `TIME` VARCHAR(8), `IP` VARCHAR(15), `BROWSER` TINYTEXT, PRIMARY KEY (id))");
foreach($form_data as $name=>$value)
{
mysqli_query($db ,"ALTER TABLE $mysql_table ADD $name VARCHAR(255)");
}
mysqli_query($db, "INSERT INTO $mysql_table (`DATESTAMP`, `TIME`, `IP`, `BROWSER`, `REFERER`)
VALUES ('".date("Y-m-d")."',
'".date("G:i:s")."',
'".$_SERVER['REMOTE_ADDR']."',
'".$_SERVER['SERVER_NAME'].$_SERVER['PHP_SELF']."',
'".$_SERVER['HTTP_USER_AGENT']."')")or die('Failed to insert data into table!<br>'.mysqli_error($db));
$id = mysqli_insert_id($db);
foreach($form_data as $name=>$value)
{
mysqli_query($db, "UPDATE $mysql_table SET $name='".mysqli_real_escape_string($db, $value)."' WHERE ID=$id") or die('Failed to update table!<br>'.mysqli_error($db));
}
mysqli_close($db);
header('Location: '.$success_url);
exit;
}
Success and Error pages are internal pages of the project. App yaml has following handler:

# TO serve static
- url: /(.*\.(html$|css$|js$|svg$|))
static_files: \1
upload: (.*\.(html$|css$|js$|svg$))
application_readable: true


# to serve all php scripts
- url: /(.+\.php)$
script: \1


Actually either the Redirect or the Cloud SQL work at a time. If we remove cloud sql part the Redirect works and if we ignore the Redirect part Cloud SQL successfully puts the data into table but then doesn't redirect. Here I'm specifically naming Cloud SQL because Redirect is working with MySQL on localhost. Please help further on how to redirect a php page with cloud sql form.

Thank you in advance.