Im having a problem here… as the title suggest, my error_tag isnt working, its simply not showing the error message:

new.html.eex

<%= form_for @changeset, Routes.category_path(@conn, :create), fn f -> %>
    <label for="category_name" class="form-label">Nome da Categoria</label>
    <%= text_input f, :name, class: "form-control", placeholder: "Nome" %>
    <%= error_tag f, :name %>
    <%= submit "Cadastrar", class: "btn btn-primary my-3" %>
<% end %>

controller

def create(conn, %{"category" => category}) do
    case Records.category_create(category) do
      {:ok, _inserted_category} ->
        conn
        |> put_flash(:info, "Categoria criada!")
        |> redirect(to: Routes.category_path(conn, :index))
      {:error, changeset} ->
        conn
        |> put_flash(:error, "Erro ao criar categoria!")
        |> render("new.html", changeset: changeset)
    end
  end

context

defdelegate category_changeset(category, params), to: Category, as: :changeset
defdelegate category_create(params), to: Category, as: :create

changeset and repo action

def changeset(%Category{} = category, params \\ %{}) do
    category
    |> cast(params, [:name])
    |> validate_required([:name])
    |> validate_length(:name, min: 3, max: 15)
    |> validate_format(:name, ~r{\S})
    |> unique_constraint(:name)
  end

  def create(params) do
    %Category{}
    |> changeset(params)
    |> Repo.insert()
  end

inspected changeset
Its working properly, the error is there!

[debug] Processing with ConfinWeb.CategoryController.index/2
  Parameters: %{}
  Pipelines: [:browser]
[debug] QUERY OK source="categories" db=15.0ms idle=407.0ms
SELECT c0."id", c0."name" FROM "categories" AS c0 []

#Ecto.Changeset<
  action: :insert,
  changes: %{},
  errors: [name: {"can't be blank", [validation: :required]}],
  data: #Confin.Records.Category<>,
  valid?: false
>

HTML generated

screenshot_20210721_175907554×140 56.9 KB