public ip address behaviour when link redundancy happens

Hello everyone,

Please i need advice on link redundancy configuration:

Fortigate 60E firmware v6.4.8

Wan1 -> Main ISP

WAN2 -> Backup ISP

Redundancy is working ok i think; when WAN1 fails, WAN2 becomes active BUT when this happens i lose all external services like mail server, nvr's, web services, all of these tied to my main ISP Public IP Address which at that moment is down.

Is there any configuration i can make to passthrough all requests made to my main ISP public address (Down) to my backup ISP(Active)?

Appreciate the help