I activated the “testing repository” and made the update for core8 - traefick. Now I was able to modify the Virtual host created previously and the validation was done without problems. By activating the “Request for a Let’s Encrypt certificate” option, I automatically obtained the certificate.
Thank you!
PS:
After these changes, I was able to install wordpress without any problem, following this tutorial: Install wordpress to NS8 - Howto - NethServer Community