virtual ip to reach internal web serveur with https . Another port different of 443

i everyone, i want to configure https access to reach my internal web access. i have configured virtual ip, i used a port different of 443. my 443 port is used for another server. i use ssl inspection with the fortigate certificate on the policy, but i cannot show the certificate in the web browser . i have used a purchased certificate for the domaine url name , but i cannot see the certificate in the browser .