Swagger / Readme / Datamodel

3 useful references / libraries are available:

Readme API Endpoints overview: https://docs.billit.be/reference . It contains the parameters and Samples in nearly 20 languages.
Swagger UI Guide https://api.billit.be/swagger/ui/index.
Datamodel Billit and relationship with Einvoice models (Peppol and other): https://docs.billit.be/docs/billit-datamodel-and-einvoice-networks

1. What is the Billit API

The Billit API allows you to programmatically interact with Billit’s services — such as invoices, clients, quotes, and payments. It is built around REST endpoints and supports standard CRUD operations (Create, Read, Update, Delete).

2. Accessing Swagger UI

Go to https://api.billit.be/swagger/ui/index
Browse all available endpoints, methods, parameters, and schemas
Use the interactive interface to test endpoints with “Explore”

3. Authentication

Most endpoints require authentication.

Use the API KEY in Swagger UI to input your credentials

4. Common API Endpoints

While the full list is in Swagger, here are examples:

Resource	How can it help you?
Account	Retrieve the context of the Account (aka company) context you are operating in. https://docs.billit.be/docs/create-new-companies
Orders	Perform create, read, update, delete, or query operations on invoices, quotes, and credit notes (both income and expense). Assigning a customer or supplier to an order will either create a new party or link the order to an existing party.
Party	Manage the customers and suppliers of an Account