AWS IoT Immersion Day Workshop:: Not able to run the CloudFormation template on trial account

Hello.

Has your AWS account used Cloud9 in the past?
If your AWS account has never used Cloud9 in the past, you may no longer be able to use it.
Cloud9 suspended access for new users on July 25, 2024.
I think that's probably what's causing the error.
https://aws.amazon.com/jp/blogs/devops/how-to-migrate-from-aws-cloud9-to-aws-ide-toolkits-or-aws-cloudshell/

After careful consideration, we have made the decision to close new customer access to AWS Cloud9, effective July 25, 2024. AWS Cloud9 existing customers can continue to use the service as normal. AWS continues to invest in security, availability, and performance improvements for AWS Cloud9, but we do not plan to introduce new features.