VPN between Z4 through meraki to forti firewall overlaps the subnets

[M.Sultan]

Hi engineers,

Trying to build site to site vpn from Z4 Meraki to forti firewall but meraki dashboard pop below messages, What would be the reason and the solution ?

The VLAN subnet 172.21.16.8/29 overlaps with a remote VPN subnet on the non-meraki peer Forti-W1 (172.16.0.0/12). IP traffic will be routed to the smallest subnet that Contains the IP address.

The subnet on the non-meraki peer Forti-W1 (172.16.0.0/12) overlaps with the subnets on networks London1 (172.21.16.0/29) and Z4 (172.21.16.16/29). IP traffic will be routed to the smallest subnet that Contains the IP address.

[Rob Ingram]

@M.Sultan this is the exact same post as - https://community.cisco.com/t5/vpn/vlan-overlaps-z4-to-forti-vpn-establishing/m-p/4953962#M291774

Change the remote network to be more specific than the /12 so there is no overlap or use NAT. You would have to change crypto ACL that defines interesting traffic on both the local side and the remote peer to use the NAT address instead of the real network.

[MHM Cisco World]

as I know the Meraki dont support NAT with VPN, 
so you need to look on Forti to NAT the LAN.
this need change ACL instead of using real IP you need to use mapped IP in ACL of VPN in Meraki and Forti FW