When I try to add my domain to my website (Addon Domain) I get this error:
Illegal characters in the naming field, please verify input. .
Invalid Domain, please check your input…
If you already chose to install WordPress with a HTTPS URL, you should consider to install an SSL certificate before, so that your visitors can access your website through HTTPS after you install WordPress.
You should copy-paste the full text that’s in the boxes in the client area, exactly as it’s displayed there. This includes the BEGIN and END lines, with all the equals signs.