P2S Azure VPN assigns invalid ips for "old school routers"

Hi!

So I have an Azure P2S VPN configured to assign IPS in the range 172.16.201.0/24

The first client that connects to the VPN gets IP 172.16.201.0

Everything works well (internet access and subnet access), however I have another IPSEC S2S tunnel and the router (a fortinet firewall) on the other end of the tunnel considers IP 172.16.201.0 to be invalid (as in the /24 range, the first IP should be .1). This means my first VPN client cannot access the machines beyond the S2S tunnel.

The next client and all of the next ones have a  >= .1 IP and access works everywhere, including beyond the S2S tunnel.

Is there a way to forbid assigning this .0 IP address?

Thank you very much!