Using actor_id in atomic Change causes sql error

Hey there I’m giving Ash my first try and like it pretty well so far. I’m trying to implement a bulk update but run into a SQL error and I can only guess the problem. I have the following Change, similar to the one in the book:

defmodule CourseManager.Chat.Changes.AddUserToSeenBy do
  use Ash.Resource.Change

  @impl true
  def init(opts), do: {:ok, opts}

  @impl true
  def atomic(_changeset, _opts, context) do
    if context.actor do
      actor_id = context.actor.id
      {:atomic,
       %{
         seen_by:
           {:atomic,
            expr(
              fragment(
                "array_prepend(?, array_remove(?, ?))",
                ^actor_id,
                seen_by,
                ^actor_id
              )
            )}
       }}
    else
      :ok
    end
  end
end

And the attribute:

    attribute :seen_by, {:array, :uuid} do
      description "Array of user IDs who have seen this message"
      default []
      public? true
    end

The bulk_update didn’t work, so I tried a single update, but I get the following error:

[debug] QUERY ERROR source="messages" db=1.5ms queue=0.3ms idle=25.3ms
UPDATE "messages" AS m0 SET "updated_at" = (CASE WHEN (array_prepend($1, array_remove(m0."seen_by"::uuid[], $2)))::uuid[] != m0."seen_by"::uuid[] THEN $3::timestamp ELSE m0."updated_at"::timestamp END)::timestamp, "seen_by" = (array_prepend($4, array_remove(m0."seen_by"::uuid[], $5)))::uuid[] WHERE (m0."id"::uuid = $6::uuid) RETURNING m0."id", m0."message", m0."deleted", m0."reactions", m0."seen_by", m0."inserted_at", m0."updated_at", m0."user_id", m0."course_id", m0."parent_message_id" ["71a3f79a-62f6-49c3-8c43-d7d82ab6fd1c", "71a3f79a-62f6-49c3-8c43-d7d82ab6fd1c", ~U[2025-07-28 16:35:28.369137Z], "71a3f79a-62f6-49c3-8c43-d7d82ab6fd1c", "71a3f79a-62f6-49c3-8c43-d7d82ab6fd1c", "b6a170f6-0373-460f-acef-77ae9e76bb72"]

When I put the query in pgadmin and applying the arguments, I only have to use single quotes to make it work correctly.

Is it possible that the PG typecheck fails because the actor_id is not passed as a uuid but as a string instead?
Can anyone give me some advice how to proceed?

Thanks