Does this work for you?  I've been trying this exact request to fulfill all items on an order, and I always get a blank response.  Other actions work, just not this one. I've also tried to get a list of fulfillments, and it always comes up {"fulfillm...

   I'm having problems creating a very simple post to fulfill and close an order using this example:https://shopify.dev/api/admin/rest/reference/shipping-and-fulfillment/fulfillment#create-2021-07POST /admin/api/2021-07/orders/450789469/fulfillments....