using System;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var invoice = new SalesInvoice()

        {

            ContactId = 201171400939013415,

            RemoveInvoiceSequenceId = true,

            InvoiceSequenceId = "F2017004",

            Reference = null,

            InvoiceDate = "5-1-2017",

            Currency = "EUR",

            PricesAreIncludingTax = false   ,

            Details = new Dictionary<string, SalesInvoiceDetailAttributes>()

        };

        invoice.Details.Add("0", new SalesInvoiceDetailAttributes()

                            {

                                    Description = "Product description",

                                    Price = 13.80M,

                                    Amount = "10",

                                    TaxRateId = 197923875808347751,

                                    LedgerAccountId = 197923875101607508

                            });

        invoice.Details.Add("1", new SalesInvoiceDetailAttributes()

                            {

                                    Description = "Product description",

                                    Price = 13.80M,

                                    Amount = "10",

                                    TaxRateId = 197923875808347751,

                                    LedgerAccountId = 197923875101607508

                            });

        Console.WriteLine(JsonConvert.SerializeObject(invoice));

    }

}

​

[JsonObject(Title = "sales_invoice")]

public class SalesInvoice

{

    [JsonProperty("contact_id")]

    public long ContactId { get; set; }

    [JsonProperty("remove_invoice_sequence_id")]

    public bool RemoveInvoiceSequenceId { get; set; }

    [JsonProperty("invoice_sequence_id")]

    public string InvoiceSequenceId { get; set; }

    [JsonProperty("reference")]

    public string Reference { get; set; }

    [JsonProperty("invoice_date")]

    public string InvoiceDate { get; set; }

    [JsonProperty("currency")]

    public string Currency { get; set; }

    [JsonProperty("prices_are_incl_tax")]

    public bool PricesAreIncludingTax { get; set; }

    [JsonProperty("details_attributes")]

    public Dictionary<string, SalesInvoiceDetailAttributes> Details { get; set; }

}

​

public class SalesInvoiceDetailAttributes

{

    [JsonProperty("description")]

    public string Description { get; set; }

    [JsonProperty("price")]

    public decimal Price { get; set; }

    [JsonProperty("amount")]

    public string Amount { get; set; }

    [JsonProperty("tax_rate_id")]

    public long TaxRateId { get; set; }

    [JsonProperty("ledger_account_id")]

    public long LedgerAccountId { get; set; }

}