(HELP) Custom variable for ENV always error

Serverless Framework
1

Hi guys,

I’m trying to use s3 service in my project.
I save costum variabel & use in my provider property

service: snapnext

custom:
  imagesBucketName: snapnext-images

provider:
  name: aws
  runtime: nodejs6.10
  iamRoleStatements: # IAM permissions granted to all functions
    - Effect: Allow
      Action:
        - S3:GetObject
      Resource:
        - Fn::Join:
            - ''
            - - 'arn:aws:s3:::'
              - '${self:custom.imagesBucketName}/*'
  environment:
    IMAGES_BUCKET_NAME: ${self:custom.imagesBucketName}

functions:
  downloadImage: # Define a new Function
    handler: functions/downloadImage.handler
    events:
      - http:
          path: images
          method: post

resources:
  Resources:
    ImagesBucket:
      Type: AWS::S3::Bucket
      Properties:
        BucketName: ${self:custom.imagesBucketName}
        AccessControl: PublicRead

plugins:
  - serverless-offline

When I’m trying to deploy, I’m always getting an error message like this

33%20PM
33%20PM1292×520 150 KB

Any idea why this happens?
And how to better way to debug in a serverless framework, especially for .yml file?

Many Thanks