I have this yaml definition and it gives the following error:

missed comma between flow collection entries

This is how my yaml looks like:

 create_bucket_lifecycle_policy:
        action: aws_boto3.boto3action
        input:
          params:
            Bucket: <% $.bucket_full_name %>
            LifecycleConfiguration: {
                                      Rules: <-- this is where error coming
                                      - {'Expiration': {'Date': <%= format(Sys.time(), "%d %B, %Y") %>}}             
                                    }
        on-success:
          - create_inline_policy
        on-error:
          - fail

can someone please help me?