At the final stage of the installation, I got to creating an administrator account, and then there was another hitch - the form seemed to be sent, but the login did not work. At first, I thought that the problem was in the browser. Then I began to blame the database. In the end, I found a guide that laid everything out on the shelves:
https://host4geeks.com/blog/install-freepbx-linux/. It describes the entire process of completing the installation and creating the first user, taking into account all the nuances. I simply repeated the steps and everything worked. If you are not creating an admin account, and the installation seems to have been successful, be sure to read this article. It saved me from reinstalling.