Passing body parameter to Swagger API datasource PUT method

What syntax do i use to pass parameters to the auto-generated body parameter "PutV0AdditivesAdditiveId"?

I need to pass two parameters, "AdditiveName" and "ValidityEnd" as defined in AdditiveResponse.
How can i do this in expression form?

Auto generated method for PUT additive:

...
    public async Task<HttpResponseMessage> PutV0AdditivesAdditiveId(Int64 additiveId, AdditiveValueParameter body)
    {
        var uri = new Uri(baseUri, $"v0/Additives/{additiveId}");

        var message = new HttpRequestMessage(HttpMethod.Put, uri);

        message.Content = new StringContent(JsonSerializer.Serialize(body), Encoding.UTF8, "application/json");

        OnPutV0AdditivesAdditiveId(message);

        var response = await httpClient.SendAsync(message);

        response.EnsureSuccessStatusCode();

        return response;
    }

AdditiveValueParameter class:

public partial class AdditiveValueParameter
{
    [JsonPropertyName("additiveName")]
    public string AdditiveName
    {
        get;
        set;
    }

    [JsonPropertyName("validityEnd")]
    public DateTime? ValidityEnd
    {
        get;
        set;
    }
}

}

You need to create an object from this class and set the object properties.

Thank you for your reply. I ended up with an expression like this:
${new AdditiveValueParameter(){AdditiveName = this.additiveresponse.AdditiveName}}

Is this according to your suggestion, and best practice?