How do I mark a scheduled fulfillment as open using shopify API?

Retired Boards Appdev Graphql Basics And Troubleshooting
1

I’m trying to do as described here https://shopify.dev/api/admin-rest/2022-07/resources/fulfillmentorder#post-fulfillment-orders-fulfillment-order-id-open but I’m always receiving a

NoMethodError: private method `open' called for #

when trying to use the open method on the fulfillment order using this code

```css
order = ShopifyAPI::Order.first(
   params: { name: "1649", status: 'any' }  
 )
fo = order.fulfillment_orders.last
fo.open