When you launch SFTP Gateway 2.001.00 from the AWS Marketplace, the CloudFormation template gives you this error:
Template format error: Conditions can only be boolean on parameters and other conditions
The template from the AWS Marketplace currently has syntax errors.
You can download correct versions of the CloudFormation templates using these links:
For the time being, use these templates instead of the ones on the AWS Marketplace.
We are in communication with AWS support, and hope this will be resolved soon.