public function activate()
    {
        // Check if we have a charge ID to use
        if (!$this->chargeId) {
            throw new Exception('Can not activate plan without a charge ID.');
        }

        // Activate and return the API response
        $this->response = $this->api->rest(
            'POST',
            "/admin/{$this->plan->typeAsString(true)}/{$this->chargeId}/activate.json"
        )->body->{$this->plan->typeAsString()};

        return $this->response;
    }