I suspect there may be a small amount of confusion between what a route and a traffic selector are. A traffic selector, which you currently have configured as 0.0.0.0/0 on the GCP side of your VPN is considered an “encryption domain”. You can also think of it like a “hall pass” which defines which traffic sources are allowed to enter or use the VPN. However, “a traffic selector is not a route”.
Once you have defined the traffic selectors and your VPN is established, you still have to tell your VPC what traffic should use the VPN as a next-hop. Defining the traffic which will be sent to the VPN is done by creating a static route for your VPC, with a next-hop of the VPN. A policy-based or route-based Classic VPN tunnel uses static routing (you have created a route-based tunnel).
From the “route-based” link above:
“If you create one of these tunnels using the Cloud Console, Google Cloud
automatically creates custom static routes based on the remote IP ranges you
specify in the Cloud VPN configuration. If you use gcloud commands to create one
of these tunnels, you must manually create the static routes that use the tunnel
as a next hop.”
This means that depending on what traffic selector you used for the far-side of the VPN (not the “NET1” side), a static route may have been created for you. However, if you used something like 0.0.0.0/0 as a traffic selector on both sides of the VPN, then this static route will not do much. To have traffic be routable through the VPN, you will likely need to define a static route in NET1 which points to the subnet in your peer VPN that you wish to communicate with. This static route will need a next-hop of the NET1 VPN.
Please note: the same is true for the far side of the VPN. A static route (in the peer VPN VPC/network) which points to the subnet in NET1 that you wish to communicate with, will need to be created with a next-hop of the “peer VPN”.
As you have already opened the firewall on both sides of the VPN, once you create appropriate static routes, you should be able to ping from a subnet in NET1 to the peer VPN subnet (provided the static routes match).