Question about contact form HTTP ERROR 405 crash

Question

so I am trying to make a link to contact form but it seems to be crashing and I do not know why is this happening. I double checked the link and variable name, but seems like error 405 happens without stopping every time I click.

This is my html part

<h3>Contact Form</h3>
<div class="containerofcontact" style="text-align: left !important;">
<form method="POST" action="contactform.php">
<label for="name">Name</label>
<input type="text" id="Name" name="Name" placeholder="Your name..">

<label for="email">Email</label>
<input type="text" id="Email" name="Email" placeholder="Your Email">

<label for="subject">Subject</label>
<textarea id="Subject" name="Subject" placeholder="Place Detail of Concern" style="height:200px"></textarea>
<input type="submit" value="Send">
</form>
</div>

This is php part

<?php
    $name = $_POST['Name'];
    $email = $_POST['Email'];
    $text = $_POST['Subject'];

    $mailTo = "blankforshare";
    $headers = "From: ".$email;
    $txt = "You have received an e-mail from ".$name."\n\n".$text;
    mail($mailTo, $headers, $txt) or die("Error!");
    header("Location: index.html");
?>

Thank you for the help.