W System / Blog
Practical notes on EU e-invoicing mandates, Peppol, VAT and EORI validation and sanctions screening, written for people who build invoicing, ERP and accounting software. New articles appear here first. Subscribe with the RSS feed.
· Zifeng Wei
From 1 January 2027 Slovak VAT payers send domestic B2B invoices as Peppol BIS 3 UBL through a certified provider. The fields the Financial Administration adds to EN 16931 (0245:DIČ endpoints, addresses, IČO, legal form, tax point date, VATEX), the timeline incl. the no-fines bill, the invoice UUID and a checklist.
· Zifeng Wei
The third BMF letter on mandatory B2B e-invoicing keeps every deadline but settles down payments (BT-113 and BT-22 until 30 June 2030), construction and gross-price invoices, corrections, business-rule errors and penalties. Paragraph by paragraph, with what to do in your software.
· Zifeng Wei
Formats for all 27 member states plus Northern Ireland, how VIES works, when you must validate, consultation numbers as proof, and what each VIES error means.
Shorter how-tos we published on our Hashnode blog before this section existed:
Written by Zifeng Wei, who builds W System, the EU e-invoicing and counterparty-check API these articles mention. Corrections are welcome at [email protected].
Facts checked 2026-10-19. W System is the maker of this product. Not affiliated with the European Commission. Not legal or tax advice.