Subiekt123 is accounting and finance software that enables issuing invoices in the National e-Invoice System (KSeF). This function makes invoicing more efficient and compliant with applicable regulations and enables full digitisation of documents. Scope: Generating e-invoices – easy creation of electronic invoices that meet KSeF requirements. KSeF integration – the program automatically connects to the National e-Invoice System, allowing error-free transmission of issued invoices to the tax offices. Document management – archiving and searching issued invoices. Verification and validation – before sending, the system automatically checks the invoices for correctness. Reporting and analysis – users can generate various reports on their invoicing.