可能原因是请求中未包含必要的字段或者格式不正确，可以参考以下示例代码进行修改：

import requests
import json

url = 'https://myacumaticasite.com/entity/Default/18.200.001/SalesOrder'

headers = {'Content-Type': 'application/json'}

payload = {
    "Type": { "value": "SO" },
    "CustomerOrder": { "value": "1001" },
    "OrderDate": { "value": "2022-01-01T00:00:00" },
    "Details": [
        {
            "InventoryID": { "value": "ITEM001" },
            "Quantity": { "value": 5 },
            "WarehouseID": { "value": "WAREHOUSE001" },
            "UnitPrice": { "value": 10 }
        }
    ]
}

response = requests.put(url, headers=headers, data=json.dumps(payload))

print(response.status_code)
print(json.loads(response.content))

在以上示例代码中，我们通过设置请求头类型为“application/json”和将payload数据转化为json字符串发送PUT请求，以创建销售订单记录。