docs: def __create(self, subscription_plan_id, **kwargs):
          """Call documentation: `/subscription/create
          <https://www.wepay.com/developer/reference/subscription#create>`_, plus
          extra keyword parameters:
          
          :keyword str access_token: will be used instead of instance's
             ``access_token``, with ``batch_mode=True`` will set `authorization`
             param to it's value.
  
          :keyword bool batch_mode: turn on/off the batch_mode, see 
             :class:`wepay.api.WePay`
  
          :keyword str batch_reference_id: `reference_id` param for batch call,
             see :class:`wepay.api.WePay`
  
          :keyword str api_version: WePay API version, see
             :class:`wepay.api.WePay`
  
          """
          params = {
              'subscription_plan_id': subscription_plan_id
          }
          return self.make_call(self.__create, params, kwargs)