CloudFormation Combine Sub - Import - Sub - aws-cloudformation

Question

I am trying to create a parameter and would like to combine !Sub and !Import several times.
Parameters:
Environment:
Description: Stackname of Environment
Type: String
Resources:
IAMRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Statement:
- Effect: Allow
Principal:
Service: '*'
Action: ['sts:AssumeRole']
Path: /
Policies:
- PolicyName: S3Files
PolicyDocument:
Statement:
- Sid: 'S3Files'
Effect: Allow
Action:
- 's3:DeleteObjectTagging'
- 's3:GetObjectRetention'
- 's3:ListMultipartUploadParts'
- 's3:PutObject'
- 's3:GetObjectAcl'
- 's3:GetObject'
- 's3:AbortMultipartUpload'
- 's3:PutObjectRetention'
- 's3:GetObjectVersionAcl'
- 's3:GetObjectTagging'
- 's3:PutObjectTagging'
- 's3:DeleteObject'
- 's3:PutObjectAcl'
- 's3:GetObjectVersion'
Resource: !Sub
- '${ARN}/*'
- ARN:
Fn::ImportValue: !Sub ${Environment}:S3:Arn
According to the documentation it should be possible, but unfortunately I always get an error message
Template contains errors.: [/Resources/IAMRole/Type/Policies/0/PolicyDocument/Statement/0/Resource/Fn::Sub/1/ARN] 'null' values are not allowed in templates
How could the UseCase work?

Answer 1

There is a space issue in the Resource section.
Resource: !Sub
- '${ARN}/*'
- ARN:
Fn::ImportValue: !Sub ${Environment}:S3:Arn
It should be
Resource: !Sub
- '${ARN}/*'
- ARN:
Fn::ImportValue: !Sub ${Environment}:S3:Arn
Note: Fn starts under N of ARN instead of A.
Explanation: With the first indentation the line with Fn::ImportValue is considered as an input for !Sub, with the second indentation it becomes the value for ARN: defined the line above it.
Side note: Use 2 spaces or 4 spaces or tabs uniformly throughout the template.