ApiGatewayRestApi - Encountered unsupported property StageName.
This error happens when the resources defined in your
serverless.yml has attributes not supported by CloudFormation. Or the resource attributes exported in the stack are not supported by CloudFormation.
For newly introduced resource attributes, they are initially available only via the AWS API, and are only later added to CloudFormation.
Double-check the attribute name against the CloudFormation documentation for the given resource. You can find all the CloudFormation supported resources and attributes over on the AWS docs.
If you want to include resources or resources with attributes that are not available to CloudFormation yet, you have to include them as custom resources. You can read more on custom resources here.