AWS SAM/CloudFormation Internal Failure when Creating a Changeset

Hello,

An "Internal Failure" error can occur due to several reasons. For example, The JSON/YAML template being passed during the CreateChangeSet operation might have a syntactical error. This error can be anything that would normally not let you create the stack, such as an extra ":" and it can lead to an "Internal Failure". I understand that the error occurred after the IAM role resource was added to your template. I recommend validating the schema of this role resource that was added to check for extraneous properties, invalid parameters being passed to the role and/or invalid characters. You might also want to use the CloudFormation Designer to quickly validate and test the template as you roll back template changes to narrow down the issue.

Additionally, please see our knowledge center article here that discusses resolving the internal failure error in CloudFormation.