Here I have been working mainly in a electronic invoicing (facturación electrónica) REST API backend (.NET Core + MariaDB). It is capable to manage all the operations as well as manage multiple companies and sectors at the same time. I I also emits offline invoices automatically when the connection with SIAT's servers fails. Daily synchronization is also automated. All operations are handled through HTTP requests, so the system could be integrated into almost any systems.Aditionally, I have been developing a frontend (Angular) as a complement. The main focus of this frontend is to allow clients manage their invoices and systems preferences.