Invoke Rest API with a custom header

I am trying to invoke a rest api. But I get 401 unauthorized. The same call works fine from C# and postman with the same token.

Here is a snippet of the code I am using:

$contentType = "application/json" 
try 
{   
    $response = Invoke-RestMethod -Uri $URL -Method Post -Headers @{Cookie = "token=xxxxxx"} -ContentType $contentType -Body $json    
    return $response.StatusCode
}
catch 
{         
    Write-Host "Error: $($_.Exception.Message)"         
    return $null     
}

This is the C# code that is working:

HttpWebRequest webRequest;
        HttpWebResponse response;
        string URL ="https://apiurl/method";
        string header ="Cookie";
        string token ="token=xxxxxx";
 
        webRequest = (HttpWebRequest)WebRequest.Create(URL);
        webRequest.Headers.Add(header, token);
        webRequest.Method = "POST";
        webRequest.ContentType = "application/json";
        using (var streamWriter = new StreamWriter(webRequest.GetRequestStream()))
        {
             var attributes= new RestAttributes();
             string json = new JavaScriptSerializer().Serialize(attributes);
             streamWriter.Write(json);
        }
        response = (HttpWebResponse)webRequest.GetResponse();
        Stream streamResponse = response.GetResponseStream();
        StreamReader streamReader = new StreamReader(streamResponse);
        string Response = streamReader.ReadToEnd();
        return response.StatusCode.ToString();

Tried encoding the token, also tried Invoke-WebRequest. Nothing works.