How to return item metadata from search API

Question

I am trying to search my sharepoint site by metadata to return all files with matching metadata in the site.

My understanding is you can't search by metadata specifically, only in a general search (which searches the metadata).

So I have a query as follows:
POST: https://graph.microsoft.com/v1.0/search/query
With body:

{
    "requests": [
        {
            "entityTypes": [
                "listItem"
            ],
            "query": {
                "queryString": "ABC999"
            },
            "fields": [
                "id",
                "listId",
                "author",
                "title",
                "JobNo"
            ]
        }
    ]
}

I am trying to get my custom column "JobNo" in the list - but no matter what I do the column is not returned.

    "value": [
        {
            "searchTerms": [
                "abc999"
            ],
            "hitsContainers": [
                {
                    "hits": [
                        {
                            "hitId": "69868747-bae4-4030-8ecb-789c7b6605f8",
                            "rank": 1,
                            "summary": "<c0>ABC999</c0> 1 1290 0 {69868747-BAE4-4030-8ECB-789C7B6605F8},7<ddd/>",
                            "resource": {
                                "@odata.type": "#microsoft.graph.listItem",
                                "fields": {
                                    "id": "AAAAAGtrIFaMpeBNi5Q5UuCSS4YHABFIEmmOvHVOl9Wj_bW_4J4AAAAAAWAAABFIEmmOvHVOl9Wj_bW_4J4ABMe7KkEAAA2",
                                    "listId": "b14c2192-d205-4bde-8d3c-6b52d5bd0dd6",
                                    "author": "Oliver;Owner Name",
                                    "title": "Service--v2---1-"
                                },
                                "id": "69868747-bae4-4030-8ecb-789c7b6605f8"
                            }
                        },
                        {
                            "hitId": "7893eea7-3ba0-4943-843a-40f71f33fb21",
                            "rank": 2,
                            "summary": "<c0>ABC999</c0> P002 1 1065 0 {7893EEA7-3BA0-4943-843A-40F71F33FB21<ddd/>",
                            "resource": {
                                "@odata.type": "#microsoft.graph.listItem",
                                "fields": {
                                    "id": "AAAAAGtrIFaMpeBNi5Q5UuCSS4YHABFIEmmOvHVOl9Wj_bW_4J4AAAAAAWAAABFIEmmOvHVOl9Wj_bW_4J4ABQXVWrQAAA2",
                                    "listId": "a5aac080-1fa9-4a2c-bf7f-f061380a53bc",
                                    "author": "Oliver;Owner Name",
                                    "title": "Service New (v1)"
                                },
                                "id": "7893eea7-3ba0-4943-843a-40f71f33fb21"
                            }
                        }
                    ],
                    "total": 2,
                    "moreResultsAvailable": false
                }
            ]
        }
    ],
    "@odata.context": "https://graph.microsoft.com/v1.0/$metadata#Collection(microsoft.graph.searchResponse)"
}

When I query the list directly, you can see the column is indeed in that list.

...snipped        
{
            "columnGroup": "Custom Columns",
            "description": "",
            "displayName": "JobNo",
            "enforceUniqueValues": false,
            "hidden": false,
            "id": "4966126c-c248-4fe0-8324-65e500ea466a",
            "indexed": false,
            "name": "JobNo",
            "readOnly": false,
            "required": false,
            "text": {
                "allowMultipleLines": false,
                "appendChangesToExistingText": false,
                "linesForEditing": 0,
                "maxLength": 255
            }
        }, 
... snipped

In the documentation here it says you can query custom columns. https://learn.microsoft.com/en-us/graph/api/resources/search-api-overview?view=graph-rest-1.0#get-selected-properties

It also says here (fields section) you can prefix with label_ to get the property. (this also doesn't work).
https://learn.microsoft.com/en-us/graph/api/resources/searchrequest?view=graph-rest-1.0

What am I missing here? This all reads like I should be able to return the document metadata from the search.

Thanks
~Ben