Error 500 : Install Quickstart Pack Joomla 6 (And How To Fix It) | Joomla Error

After installing Quickstart Pack Joomla 6 for Helix Ultimate, website shows error 500.

Server php environment is PHP 8.3.

The Challenge

A fresh extraction of the Helix Ultimate quickstart package (running on PHP 8.3 via LiteSpeed/DirectAdmin) resulted in an immediate, persistent HTTP 500 Internal Server Error.

Initial surface diagnostics eliminated common extraction culprits:

Core PHP extensions (mysqli, nd_pdo_mysql, curl, gd, zip) were verified.
File permissions were confirmed at standard 0755 for directories and 0644 for files.
Apache rewrite rules were isolated by temporarily removing the root .htaccess file, yet the 500 error persisted unabated.

The Investigation & Audit

A check of the web server error logs uncovered the exact trigger crashing the site:

PHP Fatal error: Declaration of Laminas\Diactoros\Response::withStatus(int $code, string $reasonPhrase = ''): Laminas\Diactoros\Response must be compatible with PsrExt\Http\Message\ResponseInterface::withStatus($code, $reasonPhrase = <default>) in /.../libraries/vendor/laminas/laminas-diactoros/src/Response.php on line 147

The Server Side: The hosting panel had the compiled PHP psr extension enabled. This extension forced its own built-in interface rules onto the server, which did not use strict types ($code, $reasonPhrase = <default>).

The CMS Side: Joomla’s bundled laminas-diactoros library uses strict modern PHP typing (int $code, string $reasonPhrase = '').

The Collision: PHP 8 enforces strict signature matching. Because the library's code didn't match the server extension's older, untyped definition, the PHP engine threw a fatal compatibility error and halted execution immediately.

The Solution

Disable PSR extension in PHP extensions settings.

The Results

Instant Service Restoration: Immediately upon unchecking psr, the HTTP 500 error was eliminated without requiring a single file modification or vendor patch inside the CMS.