diff --git a/.gitattributes b/.gitattributes
index 6dbe3f1..d3b69a6 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -5,3 +5,4 @@ tests/			export-ignore
 .gitattributes	export-ignore
 phpunit.xml.*	export-ignore
 composer.lock	export-ignore
+composer.phar	export-ignore
diff --git a/.gitignore b/.gitignore
index 2666cbc..b215946 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 /build/
 /vendor/
 /node_modules/
+/composer.phar
diff --git a/acp/wpn_acp_module.php b/acp/wpn_acp_module.php
index ab522b9..1471b7e 100644
--- a/acp/wpn_acp_module.php
+++ b/acp/wpn_acp_module.php
@@ -65,33 +65,28 @@ public function main($id, $mode)
 		$form_key = 'phpbb/webpushnotifications';
 		add_form_key($form_key);
 
-		switch ($mode)
+		if ($mode === 'webpush')
 		{
-			case 'webpush':
-				// Load a template from adm/style for our ACP page
-				$this->tpl_name = 'wpn_acp_settings';
+			// Load a template from adm/style for our ACP page
+			$this->tpl_name = 'wpn_acp_settings';
 
-				$this->lang->add_lang('webpushnotifications_module_acp', 'phpbb/webpushnotifications');
+			$this->lang->add_lang('webpushnotifications_module_acp', 'phpbb/webpushnotifications');
 
-				// Set the page title for our ACP page
-				$this->page_title = $this->lang->lang('ACP_WEBPUSH_SETTINGS');
+			// Set the page title for our ACP page
+			$this->page_title = $this->lang->lang('ACP_WEBPUSH_SETTINGS');
 
-				if ($this->request->is_set_post('submit'))
+			if ($this->request->is_set_post('submit'))
+			{
+				if (!check_form_key($form_key))
 				{
-					if (!check_form_key($form_key))
-					{
-						$language = $phpbb_container->get('language');
-						trigger_error($language->lang('FORM_INVALID'), E_USER_WARNING);
-					}
-
-					$this->save_settings();
+					$language = $phpbb_container->get('language');
+					trigger_error($language->lang('FORM_INVALID'), E_USER_WARNING);
 				}
 
-				$this->display_settings();
-			break;
+				$this->save_settings();
+			}
 
-			default:
-			break;
+			$this->display_settings();
 		}
 	}
 
diff --git a/adm/style/event/acp_main_notice_after.html b/adm/style/event/acp_main_notice_after.html
new file mode 100644
index 0000000..d02a23a
--- /dev/null
+++ b/adm/style/event/acp_main_notice_after.html
@@ -0,0 +1,5 @@
+{% if S_WPN_COMPATIBILITY_NOTICE %}
+	<div class="errorbox">
+		<p>{{ lang('ACP_WEBPUSH_REMOVE_NOTICE') }}</p>
+	</div>
+{% endif %}
diff --git a/adm/style/wpn_acp.js b/adm/style/wpn_acp.js
index ec860f8..32e000e 100644
--- a/adm/style/wpn_acp.js
+++ b/adm/style/wpn_acp.js
@@ -75,5 +75,5 @@ phpbb.addAjaxCallback('generate_vapid_keys', () => {
 		const privateKeyInput = document.querySelector('#webpush_vapid_private');
 		publicKeyInput.value = keyPair.publicKey;
 		privateKeyInput.value = keyPair.privateKey;
-	})
-})
+	});
+});
diff --git a/build.xml b/build.xml
index 040d0e5..9fe6aba 100644
--- a/build.xml
+++ b/build.xml
@@ -23,6 +23,8 @@
 		<delete file="${dir}/composer.phar" />
 		<delete file="${dir}/phpunit.xml.dist" />
 		<delete file="${dir}/README.md" />
+		<delete file="${dir}/package.json" />
+		<delete file="${dir}/package-lock.json" />
 	</target>
 
 	<!--
@@ -68,7 +70,7 @@
 		<if>
 			<equals arg1="${has-dependencies}" arg2="1" />
 			<then>
-				<exec dir="${package-directory}" command="php composer.phar install --no-dev"
+				<exec dir="${package-directory}" command="php ../../../../../../../../composer.phar install --no-dev"
 					  checkreturn="true" />
 			</then>
 		</if>
diff --git a/event/listener.php b/event/listener.php
index da3b414..94878d0 100644
--- a/event/listener.php
+++ b/event/listener.php
@@ -29,6 +29,7 @@ public static function getSubscribedEvents()
 		return [
 			'core.ucp_notifications_output_notification_types_modify_template_vars'	=> 'load_template_data',
 			'core.ucp_display_module_before'	=> 'load_language',
+			'core.acp_main_notice'				=> 'compatibility_notice',
 		];
 	}
 
@@ -67,7 +68,7 @@ public function __construct(controller_helper $controller_helper, form_helper $f
 	 */
 	public function load_template_data($event)
 	{
-		if ($event['method_data']['id'] == 'notification.method.phpbb.wpn.webpush')
+		if ($event['method_data']['id'] === 'notification.method.phpbb.wpn.webpush')
 		{
 			$template_ary = $event['method_data']['method']->get_ucp_template_data($this->controller_helper, $this->form_helper);
 			$this->template->assign_vars($template_ary);
@@ -76,11 +77,17 @@ public function load_template_data($event)
 
 	/**
 	 * Load language file
-	 *
-	 * @param \phpbb\event\data $event
 	 */
-	public function load_language($event)
+	public function load_language()
 	{
 		$this->language->add_lang('webpushnotifications_module_ucp', 'phpbb/webpushnotifications');
 	}
+
+	/**
+	 * Check if extension is compatible (it will not be compatible with phpBB 4)
+	 */
+	public function compatibility_notice()
+	{
+		$this->template->assign_var('S_WPN_COMPATIBILITY_NOTICE', phpbb_version_compare(PHPBB_VERSION, '4.0.0-a1', '>='));
+	}
 }
diff --git a/ext.php b/ext.php
index 22bad7b..14abf84 100644
--- a/ext.php
+++ b/ext.php
@@ -12,10 +12,78 @@
 
 /**
  * phpBB Browser Push Notifications Extension base
- *
- * It is recommended to remove this file from
- * an extension if it is not going to be used.
  */
 class ext extends \phpbb\extension\base
 {
+	/**
+	 * @var array An array of installation error messages
+	 */
+	protected $errors = [];
+
+	/**
+	 * {@inheritdoc}
+	 *
+	 * Requires phpBB 3.3.12 due to new template and core events.
+	 * Should not be installed in phpBB 4.0.0-a1 because it already has push notifications.
+	 * Requires PHP 7.3 due to 3rd party libraries included.
+	 */
+	public function is_enableable()
+	{
+		return $this->check_phpbb_version()->check_php_version()->result();
+	}
+
+	/**
+	 * Check the installed phpBB version meets this extension's requirements.
+	 *
+	 * @return \phpbb\webpushnotifications\ext
+	 */
+	protected function check_phpbb_version()
+	{
+		if (phpbb_version_compare(PHPBB_VERSION, '3.3.12-dev', '<') ||
+			phpbb_version_compare(PHPBB_VERSION, '4.0.0-a1', '>='))
+		{
+			$this->errors[] = 'PHPBB_VERSION_ERROR';
+		}
+
+		return $this;
+	}
+
+	/**
+	 * Check the server PHP version meets this extension's requirements.
+	 *
+	 * @return \phpbb\webpushnotifications\ext
+	 */
+	protected function check_php_version()
+	{
+		if (phpbb_version_compare(PHP_VERSION_ID, '70300', '<'))
+		{
+			$this->errors[] = 'PHP_VERSION_ERROR';
+		}
+
+		return $this;
+	}
+
+	/**
+	 * Return the is_enableable result. Either true, or the best enable failed
+	 * response for the current phpBB environment: array of error messages
+	 * in phpBB 3.3 or newer, false otherwise.
+	 *
+	 * @return array|bool
+	 */
+	protected function result()
+	{
+		if (empty($this->errors))
+		{
+			return true;
+		}
+
+		if (phpbb_version_compare(PHPBB_VERSION, '3.3.0-b1', '>='))
+		{
+			$language = $this->container->get('language');
+			$language->add_lang('install', 'phpbb/webpushnotifications');
+			return array_map([$language, 'lang'], $this->errors);
+		}
+
+		return false;
+	}
 }
diff --git a/language/en/info_acp_webpushnotifications.php b/language/en/info_acp_webpushnotifications.php
index 3b1250a..15d4e47 100644
--- a/language/en/info_acp_webpushnotifications.php
+++ b/language/en/info_acp_webpushnotifications.php
@@ -38,7 +38,8 @@
 //
 
 $lang = array_merge($lang, [
-	'ACP_WEBPUSH_SETTINGS'			=> 'Web Push settings',
+	'ACP_WEBPUSH_SETTINGS'				=> 'Web Push settings',
+	'ACP_WEBPUSH_REMOVE_NOTICE'			=> 'Web Push Notifications are now built-in to phpBB.<br>The extension “phpBB Browser Push Notifications” is no longer needed and should be uninstalled.<br>All settings and user preferences associated with the extension will be migrated into phpBB‘s built-in push notifications when you uninstall the extension.',
 	'LOG_CONFIG_WEBPUSH'				=> '<strong>Altered Web Push settings</strong>',
 	'LOG_WEBPUSH_MESSAGE_FAIL'			=> '<strong>Web Push message could not be sent:</strong> %s',
 	'LOG_WEBPUSH_SUBSCRIPTION_REMOVED'	=> '<strong>Removed Web Push subscription:</strong>» %s',
diff --git a/language/en/install.php b/language/en/install.php
new file mode 100644
index 0000000..07f72a3
--- /dev/null
+++ b/language/en/install.php
@@ -0,0 +1,43 @@
+<?php
+/**
+ *
+ * phpBB Browser Push Notifications. An extension for the phpBB Forum Software package.
+ *
+ * @copyright (c) 2023, phpBB Limited <https://www.phpbb.com>
+ * @license GNU General Public License, version 2 (GPL-2.0)
+ *
+ */
+
+/**
+ * DO NOT CHANGE
+ */
+if (!defined('IN_PHPBB'))
+{
+	exit;
+}
+
+if (empty($lang) || !is_array($lang))
+{
+	$lang = [];
+}
+
+// DEVELOPERS PLEASE NOTE
+//
+// All language files should use UTF-8 as their encoding and the files must not contain a BOM.
+//
+// Placeholders can now contain order information, e.g. instead of
+// 'Page %s of %s' you can (and should) write 'Page %1$s of %2$s', this allows
+// translators to re-order the output of data while ensuring it remains correct
+//
+// You do not need this where single placeholders are used, e.g. 'Message %d' is fine
+// equally where a string contains only two placeholders which are used to wrap text
+// in a url you again do not need to specify an order e.g., 'Click %sHERE%s' is fine
+//
+// Some characters you may want to copy&paste:
+// ’ » “ ” …
+//
+
+$lang = array_merge($lang, [
+	'PHPBB_VERSION_ERROR'	=> 'This extension is not compatible with your board. You must be using phpBB 3.3.12 or newer, up to but not including phpBB 4.x.x.',
+	'PHP_VERSION_ERROR'		=> 'This extension is not compatible with your server. Your server must be running PHP 7.3 or newer.',
+]);
diff --git a/migrations/add_webpush.php b/migrations/add_webpush.php
index e6a2b5c..2574a42 100644
--- a/migrations/add_webpush.php
+++ b/migrations/add_webpush.php
@@ -19,9 +19,9 @@ public function effectively_installed(): bool
 		return $this->db_tools->sql_table_exists($this->table_prefix . 'wpn_notification_push');
 	}
 
-	static public function depends_on()
+	public static function depends_on()
 	{
-			return ['\phpbb\webpushnotifications\migrations\handle_subscriptions'];
+		return ['\phpbb\webpushnotifications\migrations\handle_subscriptions'];
 	}
 
 	public function update_schema(): array
diff --git a/tests/notification/notification_method_webpush_test.php b/tests/notification/notification_method_webpush_test.php
index 062af01..604d568 100644
--- a/tests/notification/notification_method_webpush_test.php
+++ b/tests/notification/notification_method_webpush_test.php
@@ -539,7 +539,7 @@ public function test_export_data_with_migration(): void
 		$sql = "SELECT * FROM phpbb_user_notifications
 			WHERE method = '" . $this->db->sql_escape('notification.method.phpbb.wpn.webpush') . "'";
 		$result = $this->db->sql_query($sql);
-		$this->assertEquals(0, count($this->db->sql_fetchrowset($result)));
+		$this->assertCount(0, $this->db->sql_fetchrowset($result));
 		$this->db->sql_freeresult($result);
 
 		$this->assertEquals(