inAppPurchasePriceSchedules end point returns error 500

I am trying to add a price point to my newly created in app purchase entry using app store connect API.

The example wrong, but fortunately enough the documentation seems updated with the new JSON structure.

Unfortunately, I am getting an error 500 when sending the following JSON to the v1/inAppPurchasePriceSchedules endpoint:

{
    "data":
    {
        "type": "inAppPurchasePriceSchedules",
        "relationships":
        {
            "inAppPurchase":
            {
                "data":
                {
                    "type": "inAppPurchases",
                    "id": "6445658689"
                }
            },
            "manualPrices":
            {
                "data":
                [
                    {
                        "type": "inAppPurchasePrices",
                        "id": "${price1}"
                    }
                ]
            }
        }
    },
    "included":
    [
        {
            "type": "inAppPurchasePrices",
            "id": "${price1}",
            "attributes":
            {
                "startDate": null
            },
            "relationships":
            {
                "inAppPurchaseV2":
                {
                    "data":
                    {
                        "type": "inAppPurchasesV2",
                        "id": "6445658689"
                    }
                },
                "inAppPurchasePricePoint":
                {
                    "data":
                    {
                        "type": "inAppPurchasePricePoints",
                        "id": "eyJzIjoiNjQ0NTY1ODY4OSIsInQiOiJVU0EiLCJwIjoiNSJ9"
                    }
                }
            }
        }
    ]
}

I do not know why, as all the data seems to be OK.. the ids are fetched by previous calls and on the web site I can see my entry (without the pricing schedule of course..)

Any idea what might be wrong here?