IPsec VPN routing

I am using a Peplink Balance 700 to connect my branch offices via SpeedFusion VPN tunnels. I have also established an IPsec VPN connection to one of my suppliers using the same Balance 700 device to fortigate

My Goal:
I need to advertise the supplier’s remote IPsec VPN subnets to all my branch offices connected via SpeedFusion, so that my branches can reach the supplier’s network.

Current Setup:

Device: Peplink Balance 700

SpeedFusion VPN: Connected between my main site and branch offices

IPsec VPN: Established to supplier (on same Balance 700 to fortigate )