Why do I keep getting an Error 500 in my PHP Login System

Question

Underneath is the code I typed for my login system. I keep getting an ERROR 500 when I click the submit-signup button. For as far as I know I don't have any syntax errors. I absolutely don't know what I did wrong and would like you guys's advices.

I deleted the $dBUsername and $dBPassword for privacy reasons, sorry :(

The code to connect to the database: back-end/dbh.be.php

<?php

    $servername = "localhost":
    $dBUsername = "";
    $dBPassword = "";
    $dBName = "admhap_Users";

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

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

My signup page, the page you see on the website: signup.php

<?php
  require "header.php";
?>

    <main>
      <div>
        <section>
          <h1>Aanmelden</h1>
          <form action="back-end/signup.be.php" method="post">
            <input type="text" name="uid" placeholder="Gebruikersnaam...">
            <input type="text" name="mail" placeholder="E-mail...">
            <input type="password" name="ww" placeholder="Wachtwoord...">
            <input type="password" name="ww-her" placeholder="Herhaal wachtwoord...">
            <button type="submit" name="signup-submit">Aanmelden</button>
          </form>
        </section>
      </div>
    </main>

<?php 
  require "footer.php";
?>

The back-end code behind my sigup-page: back-end/signup.be.php

<?php
if (isset($_POST['signup-submit'])) { 

  require 'dbh.be.php'; 

        $username = $_POST['uid'];
    $email = $_POST['mail'];
    $password = $_POST['ww'];
    $passwordRepeat = $_POST['ww-her'];


    if (empty($username) || empty($email) || empty($password) || empty($passwordRepeat)) {      
        header("Location: ../signup.php?error=emptyfields&uid=".$username."&mail=".$email);
        exit();
    }
    else if (!filter_var($email, FILTER_VALIDATE_EMAIL) && !preg_match("/^[a-zA-Z0-9]*$/", $username)) {
        header("Location: ../signup.php?error=invalidmailuid");
        exit();
    }
    else if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        header("Location: ../signup.php?error=invalidmail&uid=".$username);
        exit();     
    }
    else if (!preg_match("/^[a-zA-Z0-9]*$/", $username)) {
        header("Location: ../signup.php?error=invaliduid&mail=".$email);
        exit();
    }
    else if ($password !== $passwordRepeat) {
        header("Location: ../signup.php?error=passwordcheck&uid=".$username."&mail=".$email);
        exit();
    }
    else {

        $sql = "SELECT gebruikersnaam FROM gebruikers WHERE gebruikersnaam=?";
        $stmt = mysqli_stmt_init($conn);
        if (!mysqli_stmt_prepare($stmt, $sql)) {
            header("Location: ../signup.php?error=sqlerror");
        exit();
        }
        else {
            mysqli_stmt_bind_param($stmt, "s", $username);
            mysqli_stmt_execute($stmt);
            mysqli_stmt_store_result($stmt);
            $resultCheck = mysqli_stmt_num_rows($stmt);
            if ($resultCheck > 0) {
                header("Location: ../signup.php?error=usertaken&mail=".$email);
                exit();
            }
            else {

                $sql = "INSERT INTO users (uidUsers, emailUsers, pwdUsers) VALUES (?, ?, ?)";
                $stmt = mysqli_stmt_init($conn);
                if (!mysqli_stmt_prepare($stmt, $sql)) {
                    header("Location: ../signup.php?error=sqlerror");
                    exit();
                }
                else{
                    $hashedPwd = password_hash($password, PASSWORD_DEFAULT);

                    mysqli_stmt_bind_param($stmt, "sss", $username, $email, $hashedPwd);
                    mysqli_stmt_execute($stmt);
                    header("Location: ../signup.php?signup=succes");
                    exit();
                }

            }
        }

    }
    mysqli_stmt_close($stmt);
    mysqli_close($conn);

}
else{
    header("Location: ../signup.php?");
    exit();
}
?>

Already a massive thank you

Answer 1

Check your code from file: back-end/dbh.be.php in the very first line

$servername = "localhost":

you are using : to terminate line instead of ; that's the main reason you are getting ERROR 500 right after you press submit button.