According to the AWS documentation:
Error starting instances: Invalid value <instance ID> for instanceId. Instance does not have a volume attached at root (/dev/sda1).
You attempted to start the instance before the VM import process and all conversion tasks were complete.
Resolution
Wait for the VM import process and all conversion tasks to completely finish, and then start the instance.
I am not sure if this is accurate though and whether it will be the only snag you run into.
The AMI image is on the road map, so we can accelerate this if you have a specific use case that requires Wanos on AWS.