code: 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;
      }
docs: Activates a plan to the shop.
  
  Example usage:
  (new BillingPlan([shop], [plan]))->setChargeId((int) request('charge_id'))->activate();
  
  @return object