The Tax Office in Czechowice-Dziedzice organized meetings and training sessions dedicated to the National e-Invoicing System for many months. Entrepreneurs learned about the principles of authentication, granting permissions, as well as issuing and receiving documents. After the mandatory implementation of the National e-Invoicing System, these topics moved from the training rooms to the daily work of companies. However, the biggest difficulty in using the program remains the issue of malfunctions and temporary errors. How to deal with them?