Why does submitting a form not work in sololearn's code playground?

Question

I was trying to use a form and check the input using some php code, but when I would submit the form, the output section would return the screen that I was on and not what it was suppose to be outputting.
This is the form and php:
<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
Name: <input type="text" name="name">
<br><br>
E-mail: <input type="text" name="email">
<br><br>
Password: <input type="text" name="password">
<input type="submit" name="submit" value="Submit">
</form>

<?php
$name = $email = $password = "";

if ($_SERVER["REQUEST_METHOD"] == "POST") {
if (empty($_POST["name"])) {
echo "Name is required";
} else {
if (!preg_match("/^[a-zA-Z ]*$/",$name)) {
echo "Only letters and white space allowed";
} else{
$name = test_input($_POST["name"]);
echo "Your name is " . $name;
}
}

if (empty($_POST["email"])) {
echo "Email is required";
} else {
if (!filter_var($_POST["email"], FILTER_VALIDATE_EMAIL)) {
echo "Invalid email format";
} else{
echo "Welcome";
}
}

if (empty($_POST["password"])) {
echo "Password is required";
} else {
echo "Come on in";
}
}

function test_input($data) {
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}
?>

Answer 1

Because we can only write html ,css and js