How to update a project using project rest api including tasks, project key members, etc

I'm trying to the update project including details (add/update tasks, add/update teammembers, add/update transaction controls,etc) in one call. This works

{

    "ProjectName": "20230725_test00011b",

    "OwningOrganizationId": 300000005695096,

    "PlanningProjectFlag": "false",

    "ProjectDescription": "14:20 Het doel van de aanpak is om snel en effectief hulp te organiseren voor gezinnen over de traditionele clustergrenzen binnen de organisatie heen. De Gemeente heeft de Erasmus Universiteit Rotterdam gevraagd om deze aanpak te onderzoeken.",

    "OwningOrganizationName": "A10 Accountmanagement, JZ en Financien",

    "ProjectStartDate": "2023-01-01",

    "ProjectEndDate": "2024-03-31",

    "TransactionControlFlag": true,

    "ProjectStatus": "02. Onderhanden",

    "ProjectDFF": [

        {

            "__FLEX_Context": "Regulier",

            "xxgrKostendrager": "99980014"

        }

    ]

}

But this gives me an error 404 Not found. This is to change the projectmgr on a given project. Can you see what I am doing wrong? I also tried using the TeamMemberId, same error. And from the calling application I do not (want to) know the internal IDs of Oracle of course. It's already a pity you have to pass PersonId rather than PersonNumber. Something that IS possible in task transaction controls :-).