E-invoicing for developers

API comparisons, format explainers and honest, sourced guides. Also in Deutsch and Ελληνικά.

• Peppol BIS 3.0, field by field: the minimal UBL invoice, explained for developers 7 min
• Zero percent, four ways: EN 16931 VAT category codes and the edge cases that fail validation 8 min
• The one-cent bug: rounding, decimals, and why your invoice totals fail EN 16931 validation 7 min
• Credit notes in EN 16931: UBL vs CII, type codes, and the sign rules that break integrations 7 min
• Storecove alternatives for developers (2026) 9 min
• The best e-invoicing APIs in 2026 — a developer’s guide 11 min