HA CARP Setup in AWS

[Trailbreaker]

Hey guys!
I was wondering if anybody has managed to get this running. There's a lot of conflicting information from what I've found regarding stuff like multicast on AWS and I'm desparately trying to think of a solution.
The setup we're trying to achieve is two instances running on the same VPC and overall master subnet.
Config sync works perfectly fine but the two firewalls can't tell which is the main or backup.

There's a good chance I'm missing something silly or this outright isn't possible but I'd love to hear some feedback