IPsec VPN over BGP IP(loopback interface)

I have two ISPs: Tata and Airtel, and I am able to establish an IPsec VPN with each ISP individually. Additionally, I have an APNIC IP pool (x.x.x.0/24) allocated to our company, and this same IP pool is being advertised by both ISPs.

I've set up a loopback interface on the firewall with the IP address x.x.x.1/255.255.255.0, and named it BGP-pool. Now, I want to create an IPsec VPN over the BGP-pool interface, so that the IPsec VPN users do not experience interruptions if one ISP goes down.

To clarify, BGP is functioning correctly, meaning if ISP1 goes down, the traffic is automatically rerouted to ISP2, and vice versa.

I am using a Fortigate 600F running OS 7.4.9, and FortiClient version 7.4.3 with Hotfix 1.8758.

Could someone please advise on how to achieve this setup.