Do not set actor and do not override getAttributedTo.

This was introduced to make interoperability with Mobilizon but it should be fixed on their side.

includes/activitypub/transformer/class-event.php

@@ -31,17 +31,6 @@ abstract class Event extends Post {
 	 */
 	protected $wp_taxonomy;
 
-	/**
-	 * Returns the User-URL of the Author of the Post.
-	 *
-	 * If `single_user` mode is enabled, the URL of the Blog-User is returned.
-	 *
-	 * @return string The User-URL.
-	 */
-	protected function get_actor(): ?string {
-		return $this->get_attributed_to();
-	}
-
 	/**
 	 * Returns the ActivityStreams 2.0 Object-Type for an Event.
 	 *

includes/activitypub/transformer/class-gatherpress.php

@@ -117,18 +117,6 @@ final class GatherPress extends Event {
 		return $attachments;
 	}
 
-	/**
-	 * Returns the User-URL of the Author of the Post.
-	 *
-	 * If `single_user` mode is enabled, the URL of the Blog-User is returned.
-	 *
-	 * @return string The User-URL.
-	 */
-	protected function get_attributed_to(): string {
-		$user = new Blog(); // todo is this correct? feels not right.
-		return $user->get_url();
-	}
-
 	/**
 	 * Determine whether the event is online.
 	 *