How I built a Norwegian VAT filing library in Java (and what nearly broke me)

After 3 years building a SaaS accounting system for the Norwegian market, I open-sourced the VAT filing module as a standalone Java library. This is what I learned. The problem If you've ever tried to integrate with Norwegian government APIs, you know the documentation is thorough — but the gap between reading the docs and actually getting it working in production is large. MVA-melding (Norwegian VAT return) looks simple on the surface: generate some XML, submit it. In reality i