If meraki sites are connected to Secure Connect via AutoVPN they will automatically be advertising to Secure Connect reachable subnets.
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When you connect a non-meraki device via IPsec you will also define the routable subnets in the configuration. Once both tunnels are connected, you would need to enable a source-destination cloud firewall rule to allow connectivity as the default private app and network rule is a deny all. then the sites would be able to communicate with each other.