REST API that generates invoices as PDFs from supplied structured details (invoice number, dates, sender/recipient, line items, payment terms), removing the need to hand-build invoice layout/rendering logic. Ships official SDKs for JS/Node, Python, C#/.NET, PHP, Go, Dart, and Android, so the API can be called with a native client in most common stacks rather than raw HTTP requests. A hosted service rather than something self-run.