acceptFulfillmentRequest mutation doesn't work

Retired Boards Appdev Graphql Basics And Troubleshooting
1

Dear shopify team
Im continue work on this service
https://shopify.dev/apps/fulfillment/fulfillment-service-apps#receiving-fulfillment_request-notifications

Very simple question

{
  shop {
    fulfillmentOrders(first:1, reverse: true) {
      edges {
        node {
          id
          fulfillAt
        }
      }
    }
  }
}

Thanks god this works and Im getting response. Because two previos steps doesn’t work as expected. And nobody answer my questions…

{
  "data": {
    "shop": {
      "fulfillmentOrders": {
        "edges": [
          {
            "node": {
              "id": "gid://shopify/FulfillmentOrder/5296517513392",
              "fulfillAt": null
            }
          }
        ]
      }
    }
  },

So, ok
Next step
acceptFulfillmentRequest

mutation acceptFulfillmentRequest($id: ID!, $message: String){
  fulfillmentOrderAcceptFulfillmentRequest(id: $id, message: $message){
    fulfillmentOrder {
      status
      requestStatus
    }
  }
}

with variables

{
  "id": "gid://shopify/FulfillmentOrder/5296386801840",
  "message": "test"
}

And result

{
  "data": {
    "fulfillmentOrderAcceptFulfillmentRequest": {
      "fulfillmentOrder": null
    }
  }
}

Guys…
Is anything works on Fulfillment service via GraphQL???
Thats third thing which i should integrate with Rest API…