Fully Qualified Domain Name - FQDN is the address for which the certificate is issued. You need to enter it to generate the CSR file.
If there is SSL protection it must include the page: https://panel.domeny.pl/przypomnij_haslo FQDN for it is "panel.domeny.pl"
FQDN does not include characters other than "0-9", "a-z", "." and "-".