Can't create In-App Purchase Review Screenshot by API

I am trying to create an In-App Purchase Review Screenshot to create a new In-App Purchase by API.

I'm following Apple's guide, but am stuck at step : "Make an image reservation with POST /v1/inAppPurchaseAppStoreReviewScreenshots (Create an In-App Purchase Review Screenshot)."

Payload example :

{
    "data": {
        "type": "inAppPurchaseAppStoreReviewScreenshots",
        "attributes": {
            "fileName": "my-screenshot.jpg",
            "fileSize": "45482"
        },
        "relationships": {
            "inAppPurchaseV2": {
                "data": {
                    "id": "1651010682",
                    "type": "inAppPurchases"
                }
            }
        }
    }
}

I always get error 409.

Exception = Client error: `POST https://api.appstoreconnect.apple.com/v1/inAppPurchaseAppStoreReviewScreenshots` resulted in a `409 Conflict` response:
{
  "errors" : [ {
    "id" : "7c813a34-37a6-49e7-be5f-699236659d0e",
    "status" : "409",
    "code" : "ENTITY_ERROR.A (truncated...)

I tried to remove V2 from inAppPurchaseV2 in relationships, but get the same error.

Has anyone succeeded by any chance?

I found the cause of the problem, it's because I was passing a string on "fileSize". By removing the quotes everything works!