Create nested JSON with dynamic keys with PHP

I get some data from an API call and I try to construct a JSON to send it back to another API.

The final JSON must look like this:

{
    "jobs": {
        "MP_OFFER_ID_1": {
            "job_id": "jobboard_reference_1",
            "url": "url_1",    
            "status": 0
        },
        "MP_OFFER_ID_2": {
            "job_id": "job_id_2",
            "url": "url_2",
            "status": 1
        },
    }
}

So under the jobs key, it's not an array of elements but a list of elements with unique keys.

And that's what I'm having trouble to get.

I actually have this JSON at the end:

{
    "jobs": [
        [
            {
                "18790674": {
                    "job_id": "0015909-18790674",
                    "url": "test",
                    "status": 1
                }
            },
            {
                "18790678": {
                    "job_id": "0015892-18790678",
                    "url": "test",
                    "status": 1
                }
            }
        ]
    ]
}

As you can see, jobs is an array (actually it's an array of array ^^) and that's not what I want here...