Thanks for the reply 
When I configured the domain I enabled compatibility mode in AWS. It is reporting version 7.10.2.
The auditbeat version I am using is definitely the OSS version 7.12.1, I made the error of using the newer version at the beginning.
I may have to move away from AWS managed and just install on EC2 for now, but that defeats what I was trying to do by handing over the admin of the servers to AWS.