AWS Application Composer was released to Public Preview during re:Invent 2022. The Developer Guide Documentation covers the basics of how to use the service, but currently there's limited guidelines on troubleshooting bugs.
When loading an existing SAM Template, the following error may appear:
An incompatible or malformed template has been detected, which means it is not accessible in Composer. Load another file.
The front-end provides no further details, but they are output into the browser console. For this error, the
INITIALIZE_PROJECT_FAILED event offers insight:
My error appeared to be related to the concurrent release of Step Functions Distributed Map, which changed some language definition in ASL around the
Map state, and may not yet be reflected in App Composer's validator.
AWS Application Composer is still in Preview, which means it's still undergoing active development, and things constantly shift about in AWS. If you find a similar error, it's worth sending feedback to the Service Team using the link in the AWS Console.