Welcome to the community @Leonidax!
Yes, you are correct. If you follow the guide and everything is set up correctly it should create a valid certificate for you. So considering that it is not, I guess there is something wrong.
I would advise using instead of the command sudo docker-compose up -d just sudo docker-compose up. You should then see the output of the services and so also any error messages which should tell you what is going wrong.
If that does not help it would probably be best to post in a traefik forum and ask for help there. I have sadly not much experience with traefik myself but they will probably have directly an idea what could be going wrong.