Juristic people or real people are able to apply for e-book via, real people with their electronic signatures or financial seals and juristic people with their financial seal from the link here https://uyg.edefter.gov.tr/edefterbasvuru
Users are able to use their financial seals that they got for electronic invoice, for the application to electronic book.
Application by post is not accepted.
However the companies wanted to become e-book users by using their own software, have to apply for sheet application after having confirmation from revenue administration.