v1 — choose this for PHP 8.2–8.4 projects, production deployments, or when you don't need the newest Bitrix24 API methods. v3 — choose this for PHP 8.4+ projects that need access to new REST API ...
KSEF REST API serves as an integration interface for the Polish National e-Invoice System (KSeF), a central repository of structured electronic invoices managed by the Ministry of Finance.