@vincent I have encountered a problem with some servers like @mitra
Actors doesn't have outbox property required by the ActivityPub https://www.w3.org/TR/activitypub/#actor-objects (the collection can be empty).
Another problem is that we cannot get the actor with Content-Type and Accept "application/ld+json; profile="https://www.w3.org/ns/activitystreams"", only with "application/activity+json". According to the specification, clients have to specify the first one https://www.w3.org/TR/activitypub/#retrieving-objects