Purchasing certification IP/FQDN

HI,

I set up firewall authentication to some policy on Fortigate.

and that have 11 VLANs interfaces.

any devices on each vlans need to pass firewall authentication.

Users always see confirm screen of Fortigate original certification before they log on authentication.

so I'm considering to install purchasing certification on Fortigate not to appear confirm screen.

but I don't have no idea about what IP/FQDN I should set on purchasing certification.

Please help me

Thanks in advance