public function setBase(RecurringBilling $recurringBase)
    {
        $baseCharge = $recurringBase->activated['recurring_application_charge'];

        if(!in_array('capped_amount', array_keys($baseCharge)))
            throw new \Exception("'capped_amount' and 'terms' must be included in the base recurring charge as an option");

        $this->baseId = $baseCharge['id'];

        return $this;
    }