@spec add_members(ExPlain.Client.t(), map()) ::
  {:ok, list()} | {:error, ExPlain.Error.t()}

Adds members (tenants or companies) to a tier.

The input map must include :tier_identifier and :member_identifiers.

@spec get_by_id(ExPlain.Client.t(), String.t()) ::
  {:ok, ExPlain.Tiers.Tier.t() | nil} | {:error, ExPlain.Error.t()}

Fetches a tier by its Plain ID. Returns {:ok, nil} if not found.

@spec list(
  ExPlain.Client.t(),
  keyword()
) ::
  {:ok, %{nodes: [ExPlain.Tiers.Tier.t()], page_info: ExPlain.PageInfo.t()}}
  | {:error, ExPlain.Error.t()}

Returns a paginated list of tiers.

@spec remove_members(ExPlain.Client.t(), map()) ::
  {:ok, :removed} | {:error, ExPlain.Error.t()}

Removes members from a tier.

The input map must include :tier_identifier and :member_identifiers.