Emails are sent only from the main page, why?

Question

PHP

Hello dear pros! And again I bow to you.
Faced a problem. I have a form with validation check and then submit.
Validation works fine, the letter is sent, but for some reason only from the main page of the site ... The call button in the header, the form in the footer, the header and footer are connected to all pages of the site. Why are emails not being sent from other pages?

<?php
header("Content-Type: text/html; charset=utf-8");
$name = htmlspecialchars($_POST["name"]);
$tel = htmlspecialchars($_POST["tel"]);
$target = htmlspecialchars($_POST["target"]);


$refferer = getenv('HTTP_REFERER');
$date=date("d.m.y"); 
$time=date("H:i");
$myemail = "[email protected]";

// Отправка письма администратору сайта
$tema = "У вас клиет";
$message_to_myemail = "Текст письма: Здесь текст письма которое читает админ сайта.
<br><br>
Модал:$target<br>
Имя: $name<br>
Телефон: $tel<br>

";

mail($myemail, $tema, $message_to_myemail, "From: Sitename <[email protected]> \r\n Reply-To: Sitename \r\n"."MIME-Version: 1.0\r\n"."Content-type: text/html; charset=utf-8\r\n" );

$f = fopen("leads.xls", "a+");
fwrite($f," <tr>");    
fwrite($f," <td>$target</td> <td>$name</td> <td>$tel</td>   <td>$date / $time</td>"); 
fwrite($f," <td>$refferer</td>");    
fwrite($f," </tr>");  
fwrite($f,"\n ");    
fclose($f);

?>

As I understand it, something needs to be added, but I'm not boom boom in PHP ;(

Answer 1

<form action="something.php" >
before something put /