Web API Power BI Query Anonymous

[Isbenji]

I am new to this and I am probably missing out on something. I am trying to query API with Power BI. I created the following Json API

let
    url = "https://api.mews-demo.com/api/connector/v1/accountingItems/getAll",
    headers = [#"Content-Type" = "application/json"],
    postData = "{
    ""ClientToken"": ""E8CD5356C7EAA47C2A00AACAD010831E4-167E8005911CE1D19EAA5261C29C6DD"",
    ""AccessToken"": ""744222C2F86B48F48798ACAD0108D37F-B326A9234EEAF5713B69769434EA4B2"",
    ""Client"": ""Ben Test"",
    ""ConsumedUtc"": {
        ""StartUtc"": ""2022-01-05T00:00:00Z"",
        ""EndUtc"": ""2022-02-10T00:00:00Z""
    },
    ""ClosedUtc"": {
        ""StartUtc"": ""2022-01-05T00:00:00Z"",
        ""EndUtc"": ""2022-02-10T00:00:00Z""
    },
    ""Extent"": {
        ""OrderItems"": true,
        ""PaymentItems"": true,
        ""CreditCardTransactions"": true
    }
    }"
    ,
    response = Web.Contents(
    url,
    [
    Headers = headers,
    Content = Text.ToBinary(postData)
    ]
    ),
    jsonResponse = Json.Document(response)
  
in
    jsonResponse

When going for anonymous authentication, I am encountering the following error response, if anyone can help me a bit to understand what is going wrong? I am not sure if it is about my Json advanced editor or the way I am trying to authenticate.

If anyone can provide assistance, please