Siverius

//я бы на вашем месте попробовал вот так для начала
        require('connect.php');
        if ($conn->connect_error) {
            die("Connection failed: " . $conn->connect_error);
        }
        if (isset($_POST['username']) && isset($_POST['password'])) {
            $username = $_POST['username'];
            $email = $_POST['email'];
            $password = $_POST['password'];

            $countUsersQuery = 'SELECT count(id) as count_users FROM users WHERE username=?';
            $query = $conn->prepare($countUsersQuery);
            $query->execute([$username]);
            $countUsersResult = $query->fetch();
            if ((int)$countUsersResult['count_users'] === 0) {
                $insertUserQuery = "
                    INSERT INTO users (`username`, `password`, `email`)
                    VALUES ('$username', '$password', '$email')";
            } else {
                echo "<script>alert('Логин уже занят')</script>";
            }

            if ($conn->query($insertUserQuery) === true) {
                header("Location: /");
            } else {
                echo "Error: " . $insertUserQuery . "<br>" . $conn->error;
            }

            $conn->close();
        }

$response = curl_exec($ch);
if ($errno = curl_errno($ch)) {
	$message = curl_strerror($errno);
	echo "cURL error ({$errno}):\n {$message}";
}
curl_close($ch);

foreach($array as $cart) {
    foreach($cart as $key => $value) { 
        $txt2 .= "<b>".$key."</b>: ".$value."%0A"; 
    }
}

var freeDelivery = {
        enabled: true,
        summa: freed()
    };

    function freed() {
        var getfree;
        $.ajax({
                method: "GET",
                url: "getfree.php",
                data: { type: "get_free", getfree:getfree }
            })
            .done(function( msg ) {
                console.log(msg);
                getfree = msg;
            })
            .fail(function() {
                alert( "error" );
            });
        return getfree;
    }

$array = [
	[1,2,3,4,5,6],
	[1,2,3,4,5],
];

$res = [];
for ($i = 0; $i < count($array); $i++) {
	for ($j = 0; $j < count($array[$i]); $j++) {
		if (empty($res[$j])) {
			$res[$j] = $array[$i][$j];
		} else {
			$res[$j] .= '-' . $array[$i][$j]; 
		}
	}
}

function formsend (e) {
    e.preventDefault();
    let error = formvalidate(form)
   
 
}

usort($array, static fn (array $a, array $b): int => -($a['app'] <=> $b['app']));