PHP sending email but not getting data from HTML Form [duplicate] - php

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empty $_POST in PHP mail()
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I am trying to get some data, like name, email, etc. from an HTML form and sending that data to my gmail. I am getting an email with 'You have recieved an email from .' and 'No Sender' and 'No subject' as the email details.
Here is the PHP:
<?php
if(isset($_POST['submit'])) {
$name = $_POST['first_name'];
$subject = $_POST['subject'];
$mailFrom = $_POST['email'];
$message = $_POST['message'];
$mailTo = "tamiroffen#gmail.com";
$headers = "From: " . $mailFrom;
$txt = "You have recieved an email from " . $name . ".\n\n" . $message;
mail($mailTo, $subject, $txt, $headers);
header("Location: index.html?mailsend");
}
?>
Here is the form section snippet of the HTML:
<form action="contact_form_process.php" method="POST">
<section id="contact" class="py-3">
<div class="container">
<div class="row">
<div class="col-md-9 mx-auto">
<div class="card p-4">
<div class="card-body">
<h3 class="text-center lato-font">Please Fill Out This Form To Contact Us</h3>
<hr>
<div class="row">
<div class="col-md-6">
<div class="form-group">
<input id="first_name" name="first_name" type="text" class="form-control" placeholder="First Name">
</div>
</div>
<div class="col-md-6">
<div class="form-group">
<input id="last_name" type="text" class="form-control" placeholder="Last Name">
</div>
</div>
<div class="col-md-6">
<div class="form-group">
<input id="email" type="text" class="form-control" placeholder="Email">
</div>
</div>
<div class="col-md-6">
<div class="form-group">
<input id="phone_num" type="text" class="form-control" placeholder="Phone Number">
</div>
</div>
<div class="col-md-12">
<div class="form-group">
<textarea class="form-control" name="" id="message" rows="10" placeholder="Message"></textarea>
</div>
</div>
</div>
</div>
<div class="card-footer">
<button type="submit" name="submit" class="btn btn-outline-success btn-block">Send</button>
</div>
</div>
</div>
</div>
</div>
</section>
</form>