REST API - PUT Call

Hello guys

We face a problem with the REST API POST Call which should update an object. Unfortunately, the response body shows "malformed data". However, the Request Header and Body are as in the Postman Collection and the selected property 1194 is 100% a text property (DataType = 1). The object is checked out correctly first through the API call, but then something goes wrong in the subsequent POST/PUT request.

Anyone could give me a hint?

Other operations like creating an object or GET requests are not a problem and work well.

Response body:

{
    "Status": 400,
    "URL": "/objects/0/305/latest/properties/1194",
    "Method": "POST",
    "Exception": {
        "Name": "ArgumentException",
        "Message": "Malformed data."
    },
    "Stack": "Error reference ID: dc3c78e6-5d15-40b3-a690-e7ecbb3231d9",
    "Message": "Malformed data.",
    "IsLoggedToVault": true,
    "IsLoggedToApplication": true,
    "ExceptionName": "ArgumentException"
}

Request Header URL:

https://{{MF_URL}}/REST/objects/0/305/latest/properties/1194?_method=PUT

Request body:

[
{
"PropertyDef": 1194,
"TypedValue": {
"DataType": 1,
"Value": "QRR"
}
}
]

Kind regards

Dario