Data not appending to file in php - php

Question

I am trying to appending emails that have signup'd to a csv file, but it shows success, whereas there is nothing in the file, nothing is appending and when i print_r the fwrite it says 15
This is my code
<form action="send.php" method="post" name="newsletter" class="">
<label class="sr-only">Email:</label>
<div class="input-group mb-2">
<input type="email" name="email" class="form-control rounded-right bg-transparent" placeholder="johndoe#example.com" aria-label="Username" aria-describedby="basic-addon1" style="border: 1px solid #bdbdbd;">
<button type="submit" class="home-signup-email-btn btn btn-blue btn-lg ml-3 rounded py-0">Sign Up</button>
</div>
</form>
$email = $_POST['email'];
//$filename = 'suscribers.txt';
//$somecontent = "$email\n";
// Let's make sure the file exists and is writable first.
$txt = '/n'.$_POST['email'].'/n';
$file = fopen('mailing_list.csv','a');
if (fwrite($file,$txt)){
// fwrite($file,$txt);
$message= "Success!. You have been added to our email list.";
$status = "success";
$data = array(
'status' => $status,
'message' => $message
);
echo json_encode($data);}
else
echo "fail";

Answer 1

Try using:
$file = 'people.txt';
// The new person to add to the file
$person = "John Smith\n";
// Write the contents to the file,
// using the FILE_APPEND flag to append the content to the end of the file
// and the LOCK_EX flag to prevent anyone else writing to the file at the same time
file_put_contents($file, $person, FILE_APPEND | LOCK_EX);

Answer 2

Use a+ mode:
Open a file for read/write. The existing data in file is preserved. File pointer starts at the end of the file. Creates a new file if the file doesn't exist
<form action="send.php" method="post" name="newsletter" class="">
<label class="sr-only">Email:</label>
<div class="input-group mb-2">
<input type="email" name="email" class="form-control rounded-right bg-transparent" placeholder="johndoe#example.com" aria-label="Username" aria-describedby="basic-addon1" style="border: 1px solid #bdbdbd;">
<button type="submit" class="home-signup-email-btn btn btn-blue btn-lg ml-3 rounded py-0">Sign Up</button>
</div>
</form>
$email = $_POST['email'];
// Let's make sure the file exists and is writable first.
$txt = '/n'.$_POST['email'].'/n';
$file = fopen('mailing_list.txt','a+');
if (fwrite($file,$txt)){
$message= "Success!. You have been added to our email list.";
$status = "success";
$data = array(
'status' => $status,
'message' => $message
);
echo json_encode($data);
fclose($file);
chmod($file, 0777);
}else {
echo "fail";
}

Answer 3

I found a solution it wasn't writing to the file because i didn't add an fclose to close the fopen