diff --git a/activitypub-event-extensions.php b/activitypub-event-extensions.php
index 42f8b48..392601a 100644
--- a/activitypub-event-extensions.php
+++ b/activitypub-event-extensions.php
@@ -11,7 +11,7 @@
  * License URI:  https://www.gnu.org/licenses/agpl-3.0.de.html
  * Requires PHP: 8.1
  *
- * ActivityPub plugin tested up to: 3.2.2
+ * Requires at least ActivityPub plugin with version >= 3.2.2. ActivityPub plugin tested up to: 3.2.2.
  *
  * @package activitypub-event-extensions
  * @license AGPL-3.0-or-later
@@ -26,6 +26,7 @@ define( 'ACTIVITYPUB_EVENT_EXTENSIONS_PLUGIN_FILE', plugin_dir_path( __FILE__ )
 define( 'ACTIVITYPUB_EVENT_EXTENSIONS_PLUGIN_URL', plugin_dir_url( __FILE__ ) );
 define( 'ACTIVITYPUB_EVENT_EXTENSIONS_PLUGIN_VERSION', current( get_file_data( __FILE__, array( 'Version' ), 'plugin' ) ) );
 define( 'ACTIVITYPUB_EVENT_EXTENSIONS_DOMAIN', 'activitypub-event-extensions' );
+define( 'ACTIVITYPUB_EVENT_EXTENSIONS_ACTIVITYPUB_PLUGIN_MIN_VERSION', '3.2.2' );
 
 // Include and register the autoloader class for automatic loading of plugin classes.
 require_once ACTIVITYPUB_EVENT_EXTENSIONS_PLUGIN_DIR . '/includes/class-autoloader.php';
diff --git a/includes/admin/class-general-admin-notices.php b/includes/admin/class-general-admin-notices.php
index a4de156..2751287 100644
--- a/includes/admin/class-general-admin-notices.php
+++ b/includes/admin/class-general-admin-notices.php
@@ -49,14 +49,31 @@ class General_Admin_Notices {
 	 */
 	public static function get_admin_notice_activitypub_plugin_not_enabled(): string {
 		return sprintf(
-			/* translators: 1: the name of the event plugin a admin notice is shown. 2: The name of the ActivityPub plugin. */
+			/* translators: 1: An URL that points to the ActivityPub plugin. */
 			_x(
 				'For the ActivityPub Event Extensions to work, you will need to install and activate the <a href="%1$s">ActivityPub</a> plugin.',
 				'admin notice',
 				'activitypub-event-extensions'
 			),
+			esc_html( self::ACTIVITYPUB_PLUGIN_URL )
+		);
+	}
+
+	/**
+	 * Admin notice when the ActivityPub plugin version is too old.
+	 *
+	 * @return string
+	 */
+	public static function get_admin_notice_activitypub_plugin_version_too_old(): string {
+		return sprintf(
+			/* translators: 1: The name of the ActivityPub plugin. 2: The minimum required version number of the ActivityPub plugin. */
+			_x(
+				'Please upgrade your <a href="%1$s">ActivityPub</a> plugin. At least version %2$s is required for the ActivityPub event extensions to work.',
+				'admin notice',
+				'activitypub-event-extensions'
+			),
 			esc_html( self::ACTIVITYPUB_PLUGIN_URL ),
-			admin_url( 'options-general.php?page=activitypub&tab=settings' )
+			esc_html( ACTIVITYPUB_EVENT_EXTENSIONS_ACTIVITYPUB_PLUGIN_MIN_VERSION )
 		);
 	}
 
@@ -67,15 +84,14 @@ class General_Admin_Notices {
 	 */
 	public static function get_admin_notice_no_supported_event_plugin_active(): string {
 		return sprintf(
-			/* translators: 1: the name of the event plugin a admin notice is shown. 2: The name of the ActivityPub plugin. */
+			/* translators: 1: An URL to the list of supported event plugins. */
 			_x(
 				'The Plugin <i>ActivityPub Event Extensions</i> is of no use, because you do not have installed and activated a supported Event Plugin.
 				<br> For a list of supported Event Plugins see  <a href="%1$s">here</a>.',
 				'admin notice',
 				'activitypub-event-extensions'
 			),
-			esc_html( self::ACTIVITYPUB_EVENT_EXTENSIONS_SUPPORTED_EVENT_PLUGINS_URL ),
-			admin_url( 'options-general.php?page=activitypub&tab=settings' )
+			esc_html( self::ACTIVITYPUB_EVENT_EXTENSIONS_SUPPORTED_EVENT_PLUGINS_URL )
 		);
 	}
 
@@ -89,6 +105,16 @@ class General_Admin_Notices {
 		echo '<div class="notice notice-warning"><p>' . \wp_kses( $notice, self::ALLOWED_HTML ) . '</p></div>';
 	}
 
+	/**
+	 * Warning if the plugin is Active and the ActivityPub plugins version is too old.
+	 *
+	 * @return void
+	 */
+	public static function activitypub_plugin_version_too_old(): void {
+		$notice = self::get_admin_notice_activitypub_plugin_version_too_old();
+		echo '<div class="notice notice-warning"><p>' . \wp_kses( $notice, self::ALLOWED_HTML ) . '</p></div>';
+	}
+
 	/**
 	 * Warning when no supported Even Plugin is installed and active.
 	 *
diff --git a/includes/class-setup.php b/includes/class-setup.php
index e075ee0..fe4f55b 100644
--- a/includes/class-setup.php
+++ b/includes/class-setup.php
@@ -37,6 +37,13 @@ class Setup {
 	 */
 	protected $activitypub_plugin_is_active = false;
 
+	/**
+	 * Keep the current version of the current ActivityPub plugin.
+	 *
+	 * @var string
+	 */
+	protected $activitypub_plugin_version = '';
+
 	/**
 	 * Holds an array of the currently activated supported event plugins.
 	 *
@@ -53,7 +60,13 @@ class Setup {
 	 */
 	protected function __construct() {
 		$this->activitypub_plugin_is_active = is_plugin_active( 'activitypub/activitypub.php' );
+		// TODO: decide whether we want to do anything at all when ActivityPub plugin is note active.
+		// if ( ! $this->activitypub_plugin_is_active ) {
+		// deactivate_plugins( ACTIVITYPUB_EVENT_EXTENSIONS_PLUGIN_FILE );
+		// return;
+		// }.
 		$this->active_event_plugins         = self::detect_active_event_plugins();
+		$this->activitypub_plugin_version   = get_file_data( WP_PLUGIN_DIR . '/activitypub/activitypub.php', array( 'Version' ) )[0];
 		$this->setup_hooks();
 	}
 
@@ -151,6 +164,12 @@ class Setup {
 			'plugin_action_links_' . ACTIVITYPUB_EVENT_EXTENSIONS_PLUGIN_BASENAME,
 			array( Settings_Page::class, 'settings_link' )
 		);
+
+		// Check if the minimum required version of the ActivityPub plugin is installed.
+		if ( version_compare( $this->activitypub_plugin_version, ACTIVITYPUB_EVENT_EXTENSIONS_ACTIVITYPUB_PLUGIN_MIN_VERSION ) ) {
+			return;
+		}
+
 		add_filter( 'activitypub_transformer', array( $this, 'register_activitypub_event_transformer' ), 10, 3 );
 	}
 
@@ -183,11 +202,14 @@ class Setup {
 			new Event_Plugin_Admin_Notices( $event_plugin );
 		}
 		// Check if any general admin notices are needed and add actions to insert the needed admin notices.
-
 		if ( ! $this->activitypub_plugin_is_active ) {
 			// The ActivityPub plugin is not active.
 			add_action( 'admin_notices', array( 'Activitypub_Event_Extensions\Admin\General_Admin_Notices', 'activitypub_plugin_not_enabled' ), 10, 1 );
 		}
+		if ( version_compare( $this->activitypub_plugin_version, ACTIVITYPUB_EVENT_EXTENSIONS_ACTIVITYPUB_PLUGIN_MIN_VERSION ) ) {
+			// The ActivityPub plugin is too old.
+			add_action( 'admin_notices', array( 'Activitypub_Event_Extensions\Admin\General_Admin_Notices', 'activitypub_plugin_version_too_old' ), 10, 1 );
+		}
 		if ( empty( $this->active_event_plugins ) ) {
 			// No supported Event Plugin is active.
 			add_action( 'admin_notices', array( 'Activitypub_Event_Extensions\Admin\General_Admin_Notices', 'no_supported_event_plugin_active' ), 10, 1 );