Amazon EU - automatic VAT invoices.

Situation

The client sells on Amazon in five EU markets and keeps sales documents in Subiekt nexo PRO (a Polish ERP) on a computer at the company. Every order needs an invoice with the right country and VAT rate, and there are hundreds of orders a month.

The question was: can the invoices create themselves, in the same Subiekt the accounting team works in.

What was not working

Amazon provides a panel and reports, Subiekt provides an invoice window. Between them sat a human.

• Someone went through orders market by market, determined the delivery country and VAT rate and retyped the invoice into Subiekt.
• Five markets meant five views and five sets of rates; easy to make a mistake or invoice an order twice.
• The work grew with sales, and accounting received documents late.

What we built

A C# .NET WPF desktop application on the same machine as Subiekt nexo PRO, with no cloud server and no middleman on a subscription. It talks to Amazon SP-API on one side and to Sfera (the Subiekt SDK) on the other, and keeps its own state in MS SQL.

• Order retrieval from five EU marketplaces through SP-API, in one application.
• Transaction classification: country and VAT rate determined for every order according to rules written down with the client's accountants.
• Sales invoice (FS) created in Subiekt through Sfera, with the customer, line items and the rate matched to the country.
• Dashboard: how many invoices were created, breakdown per country, classification result and a list of cases for a human to decide.

Amazon security review

An application that reads orders also reads buyer data: name, address, contact details. Before allowing it into production, Amazon checks how the application stores that data, who has access to it and how long it is kept. Without that review the integration would have stayed in testing.

We built Amazon's requirements in from the first week, before the first table in MS SQL existed.

How it works day to day

The application periodically asks SP-API for new orders from each of the five markets. Each one gets classified, then the application matches the customer and line items in Subiekt and creates an FS through Sfera.

The Amazon order ID is stored in MS SQL together with the invoice number. If the same order comes back from the API a second time, the application recognizes it and does not create a second document. An order that cannot be classified unambiguously goes to the exceptions list in the dashboard, not into Subiekt with a random rate.

Results

One hundred percent of sales invoices for Amazon orders are created without manual work, across all five markets. From kick-off to production took 3 weeks, security review included.

The code and the database belong to the client, on their own computer, with no subscription for a middleman.

What we learned

We wrote down the classification rules with the client's accountants before writing code. Country and VAT rate are tax decisions, not programming ones; our job is to apply them without exceptions and to flag when a rule does not fit.

And a dose of honesty: if you sell on one market and manual invoicing takes an hour a week, an off-the-shelf integrator on a subscription will probably do. Here, five countries, different VAT rates and Subiekt nexo PRO on a computer at the company rather than in the cloud were what settled the case for custom code.