Hello again, I made some progress
I added this line in my controller (BankErrorWeb.ApiSupportController):
require Protocol
Protocol.derive(Jason.Encoder, BankError.ClientApi.Support.SupportSchema, only: [:title, :description, :type, :status, :code, :users, :blog_posts])
after adding top line code in my controller I added @derive {Jason.Encoder, only: [..]} into my schema files that were connected like, (users, blog_posts, support_replies)
it works but it has a problem, because I don’t input support_replies: {c, users: d} in my preload, I mean
Protocol.derive(Jason.Encoder, BankError.ClientApi.Support.SupportSchema, only: [:title, :description, :type, :status, :code, :users, :blog_posts, :support_replies])
if support_replies added !!! 
it shows me this error:
** (exit) an exception was raised:
** (Protocol.UndefinedError) protocol Jason.Encoder not implemented for %BankError.Support.SupportReplySchema{__meta__: #Ecto.Schema.Metadata<:loaded, "support_replies">
def show_support_with_code(code, user_id) do
query = from u in SupportSchema,
where: u.code == ^code,
join: a in assoc(u, :users),
where: a.id == ^user_id,
left_join: b in assoc(u, :blog_posts),
left_join: c in assoc(u, :support_replies),
left_join: d in assoc(c, :users),
order_by: [desc: c.inserted_at],
preload: [users: a, blog_posts: b, support_replies: {c, users: d}]
case Repo.one(query) do
nil -> {:error, :show_support_with_code}
info -> {:ok, :show_support_with_code, info}
end
end
update
it is fixed, I had a bad schema relation
Thanks