So I am trying to make redirection after submitting the form to the home page. Fine, it works BUT there is one problem. The message is not displayed as user presses "Submit" button but is instantly redirected to the Home page. How can I make it so users first recieve "Thank you" message and than are redirected to the Home page?

<?php
$field_name = $_POST['cf_name'];
$field_email = $_POST['cf_email'];
$field_message = $_POST['cf_message'];

$mail_to = 'vladozabunov@gmail.com';
$subject = 'Message from a site visitor '.$field_name;

$body_message = 'From: '.$field_name."\n";
$body_message .= 'E-mail: '.$field_email."\n";
$body_message .= 'Message: '.$field_message;

$headers = 'From: '.$field_email."\r\n";
$headers .= 'Reply-To: '.$field_email."\r\n";

$mail_status = mail($mail_to, $subject, $body_message, $headers);

if ($mail_status) { ?>
<script language="javascript" type="text/javascript">
alert('Thank you for the message. We will contact you shortly.');
window.location = 'contact_page.html';
</script>
<?php
}
else { ?>
<script language="javascript" type="text/javascript">
alert('Message failed. Please, send an email to gordon@template-help.com');
window.location = 'contact_page.html';
</script>
<?php
}
header('Location: https://saprs.000webhostapp.com/index.html');
?>