diff --git a/admin/class-robotstxt-manager-settings.php b/admin/class-robotstxt-manager-settings.php
index 1c2d7ac..6e54620 100644
--- a/admin/class-robotstxt-manager-settings.php
+++ b/admin/class-robotstxt-manager-settings.php
@@ -333,6 +333,20 @@ class Robotstxt_Manager_Settings {
 			return is_string( $raw ) ? $raw : '';
 		}
 
+		// Account keys are UUIDs issued by the store; reject anything that
+		// cannot be one rather than storing a mangled key that only fails
+		// later at connection time.
+		if ( ! preg_match( '/^[a-f0-9][a-f0-9-]{7,126}$/i', $plain ) ) {
+			add_settings_error(
+				'robotstxt_manager_api_key',
+				'invalid_api_key',
+				esc_html__( 'The API key format is invalid. Copy the full key from your ROBOTSTXT account page.', 'robotstxt-manager' )
+			);
+
+			$raw = get_option( 'robotstxt_manager_api_key', '' );
+			return is_string( $raw ) ? $raw : '';
+		}
+
 		delete_transient( 'robotstxt_manager_catalog' );
 
 		return Robotstxt_Manager_Encryption::encrypt( $plain );
diff --git a/changelog.txt b/changelog.txt
index e14081a..24095ca 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -1,5 +1,30 @@
 == Changelog ==
 
+= 0.5.1 =
+
+_Release date: 2026-08-15_
+
+**Highlights**
+
+* Stabilization release after a full code + security audit (fresh-context review per AGENTS-deploy.md) and full-range compatibility scans (PHPCompatibility 5.6–8.5, wp-compat laddering). Declared requirements now match the real floors: **WordPress 4.4+** (was 4.7) and **PHP 8.0+** (was 7.4 — the updater's `mixed` type hints and `str_contains()` require 8.0; previously under-declared, which would have been a fatal on 7.4).
+
+**Fixed**
+
+* `test_connection()` reported "Connected." on non-200 responses and `get_catalog()` cached auth failures as an empty catalog for the full TTL. Both now check the HTTP status; non-200 responses return an error/empty and are never cached.
+* `site_domain()` used `ltrim( $host, 'www.' )`, which strips a character set and mangles hosts starting with `w` (e.g. `webdev.example.com` → `ebdev…`, breaking premium package URLs). Now strips only the literal `www.` prefix.
+* Native-update integration no longer injects premium `response` entries when no decryptable API key exists (the native updater would download into a 403).
+* Opt-in uninstall: also deletes the `update_plugins` site transient (premium entries embed the API key in the package URL — the plaintext copy must not outlive the plugin) and stops deleting a phantom `robotstxt_manager_db_version` option nothing ever wrote.
+
+**Changed**
+
+* API-key setting validates the format (UUID-like, 8–127 chars) before storing, rejecting mangled input at save time instead of failing later at connection time.
+* Plugin version 0.5.0 → 0.5.1. No database schema changes (no custom tables).
+
+**Compatibility**
+
+* WordPress: 4.4 - 7.1 (scan-verified: wp-compat clean from 4.4)
+* PHP: 8.0 - 8.5 (scan-verified: PHPCompatibility + manual feature audit)
+
 = 0.5.0 =
 
 _Release date: 2026-08-14_
diff --git a/includes/class-robotstxt-manager-core-client.php b/includes/class-robotstxt-manager-core-client.php
index 6fc3af6..ce39709 100644
--- a/includes/class-robotstxt-manager-core-client.php
+++ b/includes/class-robotstxt-manager-core-client.php
@@ -146,8 +146,18 @@ class Robotstxt_Manager_Core_Client {
 			);
 		}
 
-		$body  = wp_remote_retrieve_body( $response );
-		$count = is_array( json_decode( $body, true ) ) ? count( json_decode( $body, true ) ) : 0;
+		$code = (int) wp_remote_retrieve_response_code( $response );
+
+		if ( 200 !== $code ) {
+			return array(
+				'ok'      => false,
+				/* translators: %d: HTTP status code. */
+				'message' => sprintf( __( 'The store responded with HTTP %d. Check the Store URL and API key.', 'robotstxt-manager' ), $code ),
+			);
+		}
+
+		$decoded = json_decode( wp_remote_retrieve_body( $response ), true );
+		$count   = is_array( $decoded ) ? count( $decoded ) : 0;
 
 		return array(
 			'ok'            => true,
@@ -191,6 +201,12 @@ class Robotstxt_Manager_Core_Client {
 			return array();
 		}
 
+		// A non-200 response (auth failure, outage) must not be cached as an
+		// "empty catalog" for the full TTL — return nothing and retry next time.
+		if ( 200 !== (int) wp_remote_retrieve_response_code( $response ) ) {
+			return array();
+		}
+
 		$body = wp_remote_retrieve_body( $response );
 		$data = json_decode( $body, true );
 
diff --git a/includes/class-robotstxt-manager-updater.php b/includes/class-robotstxt-manager-updater.php
index bd98198..ca8a746 100644
--- a/includes/class-robotstxt-manager-updater.php
+++ b/includes/class-robotstxt-manager-updater.php
@@ -92,6 +92,13 @@ class Robotstxt_Manager_Updater {
 			}
 
 			if ( version_compare( $version, $new_version, '<' ) ) {
+				// Premium updates need the account key in the package URL;
+				// without a usable key the native updater would only hit a
+				// 403, so skip injecting the entry.
+				if ( 'premium' === $entry['type'] && ! $this->has_api_key() ) {
+					continue;
+				}
+
 				if ( property_exists( $transient, 'response' ) && is_array( $transient->response ) ) {
 					$transient->response[ $plugin_file ] = $this->build_update_object( $slug, (string) $plugin_file, $entry );
 				}
@@ -260,6 +267,18 @@ class Robotstxt_Manager_Updater {
 		return (object) $data;
 	}
 
+	/**
+	 * Returns whether a decryptable account API key is configured.
+	 *
+	 * @return bool True when a usable key exists.
+	 */
+	private function has_api_key(): bool {
+		$api_key_raw = get_option( 'robotstxt_manager_api_key', '' );
+		$api_key     = is_string( $api_key_raw ) ? Robotstxt_Manager_Encryption::decrypt( $api_key_raw ) : '';
+
+		return '' !== $api_key;
+	}
+
 	/**
 	 * Builds the download package URL for the native upgrader.
 	 *
@@ -298,9 +317,10 @@ class Robotstxt_Manager_Updater {
 	 * @return string Domain (e.g. 'example.com').
 	 */
 	private function site_domain(): string {
-		$host = (string) wp_parse_url( home_url(), PHP_URL_HOST );
+		$host = strtolower( (string) wp_parse_url( home_url(), PHP_URL_HOST ) );
 
-		return strtolower( ltrim( $host, 'www.' ) );
+		// Strip the literal "www." prefix (ltrim would eat any leading w/.).
+		return (string) preg_replace( '/^www\./', '', $host );
 	}
 
 	/**
diff --git a/readme.txt b/readme.txt
index 555ab09..2766b7c 100644
--- a/readme.txt
+++ b/readme.txt
@@ -1,11 +1,11 @@
 === Manager (by ROBOTSTXT) ===
 Contributors: javiercasares, robotstxt
 Tags: dashboard, catalog, updates, subscriptions, management
-Requires at least: 4.7
+Requires at least: 4.4
 Tested up to: 7.1
-Stable tag: 0.5.0
-Requires PHP: 7.4
-Version: 0.5.0
+Stable tag: 0.5.1
+Requires PHP: 8.0
+Version: 0.5.1
 License: GPL-3.0-or-later
 License URI: https://www.gnu.org/licenses/gpl-3.0.txt
 
@@ -72,7 +72,7 @@ No. This plugin is intentionally not compatible with WordPress Multisite, matchi
 
 = What PHP version is required? =
 
-PHP 8.4 or higher.
+PHP 8.0 or higher.
 
 = Do I need Plugins Core installed on my site? =
 
@@ -84,11 +84,22 @@ Encrypted at rest using AES-256-CBC with a key derived from your site's WordPres
 
 == Compatibility ==
 
-* WordPress: 4.7 - 7.1
-* PHP: 7.4 - 8.5
+* WordPress: 4.4 - 7.1
+* PHP: 8.0 - 8.5
 
 == Changelog ==
 
+= 0.5.1 =
+
+_Release date: 2026-08-15_
+
+* Stabilization release: full code/security audit, compatibility scans, and documentation alignment. Real floors declared: WordPress 4.4+, PHP 8.0+ (previously declared 4.7/7.4).
+* Connection test and catalog fetch now check the HTTP status code — an unauthorized or failing store reports an error instead of "Connected" / an empty catalog (non-200 responses are no longer cached).
+* API-key field validates the key format before storing.
+* Premium plugins are not offered as native updates when no API key is configured (they would only fail with HTTP 403).
+* Domain normalization for premium package URLs strips only the literal `www.` prefix (hosts starting with "w" were mangled).
+* Opt-in uninstall now also purges the WordPress update transient (premium entries carry the API key in their package URL) and drops a phantom option.
+
 = 0.5.0 =
 
 _Release date: 2026-08-14_
diff --git a/robotstxt-manager.php b/robotstxt-manager.php
index 69a2643..dbf7d6d 100644
--- a/robotstxt-manager.php
+++ b/robotstxt-manager.php
@@ -3,9 +3,9 @@
  * Plugin Name:       Manager (by ROBOTSTXT)
  * Plugin URI:        https://git.robotstxt.es/ROBOTSTXT/robotstxt-manager
  * Description:       Client-side dashboard for the ROBOTSTXT plugin ecosystem. Lists the catalog from a remote Plugins Core install, resolves local install/update state, and installs, activates, and updates plugins directly from the store.
- * Version:           0.5.0
- * Requires at least: 4.7
- * Requires PHP:      7.4
+ * Version:           0.5.1
+ * Requires at least: 4.4
+ * Requires PHP:      8.0
  * Author:            ROBOTSTXT
  * Author URI:        https://www.robotstxt.es/
  * License:           GPL-3.0-or-later
@@ -21,7 +21,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 }
 
 /** Plugin version. */
-define( 'ROBOTSTXT_MANAGER_VERSION', '0.5.0' );
+define( 'ROBOTSTXT_MANAGER_VERSION', '0.5.1' );
 
 /** Absolute path to the plugin directory, with trailing slash. */
 define( 'ROBOTSTXT_MANAGER_DIR', plugin_dir_path( __FILE__ ) );
diff --git a/uninstall.php b/uninstall.php
index fdf86d4..2f75539 100644
--- a/uninstall.php
+++ b/uninstall.php
@@ -18,7 +18,6 @@ $option_keys = array(
 	'robotstxt_manager_api_key',
 	'robotstxt_manager_cache_ttl_minutes',
 	'robotstxt_manager_delete_data_on_uninstall',
-	'robotstxt_manager_db_version',
 );
 
 foreach ( $option_keys as $key ) {
@@ -26,3 +25,7 @@ foreach ( $option_keys as $key ) {
 }
 
 delete_transient( 'robotstxt_manager_catalog' );
+
+// Purge the WordPress update transient: premium entries carry the API key
+// in their package URL. WordPress rebuilds it on the next update check.
+delete_site_transient( 'update_plugins' );
diff --git a/vendor/autoload.php b/vendor/autoload.php
index 30d2faf..38a9b43 100644
--- a/vendor/autoload.php
+++ b/vendor/autoload.php
@@ -19,4 +19,4 @@ if (PHP_VERSION_ID < 50600) {
 
 require_once __DIR__ . '/composer/autoload_real.php';
 
-return ComposerAutoloaderInit21193cc5ee16adfbe1fcd1cc267e45ef::getLoader();
+return ComposerAutoloaderInit891e1a90cdf8723a2ca296aab35c6101::getLoader();
diff --git a/vendor/composer/autoload_real.php b/vendor/composer/autoload_real.php
index d53f30b..036374e 100644
--- a/vendor/composer/autoload_real.php
+++ b/vendor/composer/autoload_real.php
@@ -2,7 +2,7 @@
 
 // autoload_real.php @generated by Composer
 
-class ComposerAutoloaderInit21193cc5ee16adfbe1fcd1cc267e45ef
+class ComposerAutoloaderInit891e1a90cdf8723a2ca296aab35c6101
 {
     private static $loader;
 
@@ -24,12 +24,12 @@ class ComposerAutoloaderInit21193cc5ee16adfbe1fcd1cc267e45ef
 
         require __DIR__ . '/platform_check.php';
 
-        spl_autoload_register(array('ComposerAutoloaderInit21193cc5ee16adfbe1fcd1cc267e45ef', 'loadClassLoader'), true, true);
+        spl_autoload_register(array('ComposerAutoloaderInit891e1a90cdf8723a2ca296aab35c6101', 'loadClassLoader'), true, true);
         self::$loader = $loader = new \Composer\Autoload\ClassLoader(\dirname(__DIR__));
-        spl_autoload_unregister(array('ComposerAutoloaderInit21193cc5ee16adfbe1fcd1cc267e45ef', 'loadClassLoader'));
+        spl_autoload_unregister(array('ComposerAutoloaderInit891e1a90cdf8723a2ca296aab35c6101', 'loadClassLoader'));
 
         require __DIR__ . '/autoload_static.php';
-        call_user_func(\Composer\Autoload\ComposerStaticInit21193cc5ee16adfbe1fcd1cc267e45ef::getInitializer($loader));
+        call_user_func(\Composer\Autoload\ComposerStaticInit891e1a90cdf8723a2ca296aab35c6101::getInitializer($loader));
 
         $loader->register(true);
 
diff --git a/vendor/composer/autoload_static.php b/vendor/composer/autoload_static.php
index 7d5ea49..d8902c3 100644
--- a/vendor/composer/autoload_static.php
+++ b/vendor/composer/autoload_static.php
@@ -4,7 +4,7 @@
 
 namespace Composer\Autoload;
 
-class ComposerStaticInit21193cc5ee16adfbe1fcd1cc267e45ef
+class ComposerStaticInit891e1a90cdf8723a2ca296aab35c6101
 {
     public static $classMap = array (
         'Composer\\InstalledVersions' => __DIR__ . '/..' . '/composer/InstalledVersions.php',
@@ -22,7 +22,7 @@ class ComposerStaticInit21193cc5ee16adfbe1fcd1cc267e45ef
     public static function getInitializer(ClassLoader $loader)
     {
         return \Closure::bind(function () use ($loader) {
-            $loader->classMap = ComposerStaticInit21193cc5ee16adfbe1fcd1cc267e45ef::$classMap;
+            $loader->classMap = ComposerStaticInit891e1a90cdf8723a2ca296aab35c6101::$classMap;
 
         }, null, ClassLoader::class);
     }
diff --git a/vendor/composer/platform_check.php b/vendor/composer/platform_check.php
index d2225c7..a70ba47 100644
--- a/vendor/composer/platform_check.php
+++ b/vendor/composer/platform_check.php
@@ -4,8 +4,8 @@
 
 $issues = array();
 
-if (!(PHP_VERSION_ID >= 70400)) {
-    $issues[] = 'Your Composer dependencies require a PHP version ">= 7.4.0". You are running ' . PHP_VERSION . '.';
+if (!(PHP_VERSION_ID >= 80000)) {
+    $issues[] = 'Your Composer dependencies require a PHP version ">= 8.0.0". You are running ' . PHP_VERSION . '.';
 }
 
 if ($issues) {