I have two projects 1 and 2 and two vpc networks vpc1 and vpc2 in the respective projects. I need to connect to sql instance in vpc2 (project2) from vm in vpc1 project1 using private IP. After trying diiferent methods and exploring options like vpc peering, cloud NAT (which wouldn't work for me) I found the cloud VPN solution. I am following this google docs link to connect to cloudSQL instance using its private IP. I have setup VPN Tunneling and all the necessary steps that were mentioned in the steps 1 and 2 in the link itself, but not able to connect to the instance. I have tested the VPN connectivity as well. I am able to ping a vm2 in vpc2 (project2) from vm1 in vpc1 (project1).
I suspect the problem is in the final steps over here: (https://i.stack.imgur.com/ecjzN.png)
No problem in step a and step b is also clear, but what exactly needs to be done in step c is not clear. Can you explain what exactly needs to be done over there.