Hi @Dan_Bardsley,
I've edited your above posts to only show the first 6 characters of you cluster ID for security purposes.
Using the https://github.com/elastic/found-shield-example example, I have added an internal user to your cluster and tested with that user and it works as expected with the following:
mvn clean compile exec:java -Dhost=d44312.eu-west-1.aws.found.io -Dxpack.security.user='<username>:<password>
I then used your example username and password and I get the following error unable to authenticate user [user.name].
Can you run the example with a username and password that you know the details (I'm assuming you might not have provided the username/password details for security).