I hate php help plz

I'm making a chat feature for site and php is shit code:

<?php
if (isset($_POST['send'])) {

    require 'database.php';

    $input = $_POST['input'];

 }  else {

          $sql = "INSERT INTO chatsys (chat) VALUES (?)";
          $stmt = mysqli_stmt_init($conn);
          if (!mysqli_stmt_prepare($stmt, $sql)) {
            header("index.html?error=sqlerror");
            exit();
          }
          else {

            mysqli_stmt_bind_param($stmt, "sss", $input);
            mysqli_stmt_execute($stmt);
            header("index.html?request=success");
            exit();
          }
    }
  {
    mysqli_stmt_close($stmt);
    mysqli_close($conn);

}

And database code:

<?php

$servername = "localhost";
$dBUsername = "root";
$dBPassword = "";
$dBName = "chatsys";

$conn = mysqli_connect($servername, $dBUsername, $dBPassword, $dBName);

if (!$conn) {
    die("Connection failed: ".mysqli_connect_error());
}
?>

What have I done wrong, plz I need some help. Also for context this is made to browser chat application for well sending messages between people. I am mostly writing this part because i won't let me post it if I do not write more text but like please help though.