Create two local network

I have to create to separated local network for a project

something like this

So I logged in my gateway administrator page and I activated the guest net. Now I have my main network and a second network for guest. I tried to connect a raspi 3 B+ through ethernet to the main network and through wifi to the guest network. If I try to ping a device on the main network it can be reach, but devices on the guest network cannot. If I run ifconfig on raspi I can see that there is an IP for wlan interface and an other IP for eth interface and I can ping only the eth interface IP.

It's required to create also a gateway running on raspi. After some research on the internet I found nothing that could help me. I don't know where to start.

Could someone help me with some advice?

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