Render specific partial

I'm trying to do a tag that render a specific partial:

render(partial: "user/subscriptions/subscribable_box",
            locals: { subscribable: context.environments.first['current_site'],
                          title: I18n.t("gsubscribable_box.title") })

but I can't because I don't have registers in the controller and I'm trying to execute context.render...

# frozen_string_literal: true

class RenderSubscribableBox < Liquid::Tag
  def initialize(tag_name, params, tokens)
    super
  end

  def render(context)
    context.render(partial: "user/subscriptions/subscribable_box", locals: { subscribable: context.environments.first['current_site'], title: I18n.t("gsubscribable_box.title") })
  end
end

Liquid::Template.register_tag("render_subscribable_box", RenderSubscribableBox)

I tried the:

context.registers[:controller].render(partial: "user/subscriptions/subscribable_box", locals: { subscribable: context.environments.first['current_site'], title: I18n.t("subscribable_box.title") })

but it gives me back:

*** NoMethodError Exception: undefined method render' for nil:NilClass
`

How can I create a tag for a specific partial?

Thanks a lot

Start by tracing how the custom Liquid::Tag receives its context and how context.registers is populated during rendering. Investigate the render(context) method and the attempted context.registers[:controller] access; done means establishing whether a tag can render the requested partial or documenting the supported approach.