Trying to setup default route/full tunnel mode with AWS

Hi all! I’ve followed this post to set up zerotier VPN with my AWS VPC: ZeroTier to Amazon VPC Gateway
This has worked great so far.
I’m now trying to setup full tunnel mode where all internet traffic from devices in my zerotier network flows through my aws network. I’m using this tutorial:Overriding Default Route.
For the life of me I can’t get this to work. When I check “allow default router override” on my test machine (tried windows and mac), all internet traffic stops. Things I’ve tried so far:

1)I added the iptables rules to the initial ec2 server I created to connect to my aws vpc. I added a route 0.0.0.0/0 via 172.27.0.1(the aws box in my zerotier network)
2) I created an additional ec2 instance, connected to the zerotier network, and set it up following the 2nd tutorial above. I created a 0.0.0.0/0 via 172.27.0.2 in this scenario. still nothing.

When I try to troubleshoot, all pings and traceroutes just time out. Any advice or things to try would be greatly appreciated! I’m not sure this is even possible using an ec2 instance in a vpc as the edge router. I would love to hear from someone who has been able to make this work.