Getting the error `Bucket name should not contain uppercase characters` when creating S3 buckets using serverless

I wrote a serverless.yml where I create 3 S3 bucket resources. This is some take home project I have to complete and it requires two buckets for static templates I have to process and one bucket for the results. I am defining SQS and it successfully created the queue and I was able to send messages to it from my lambda and receive messages by another lambda.

However, defining S3 bucket resources gives me An error occurred: S3LanguageTemplatesBucket - Bucket name should not contain uppercase characters.

I tried to use hard-coded values for bucket names but it didn't help.

The content of my serverless.yml file as follows:

service: process-scores

org: osano

frameworkVersion: '2'

provider:
  name: aws
  runtime: nodejs12.x
  profile: serverless-admin
  region: us-east-1
  environment:
    SQS_URL: MyQueue
    S3_HTML_TEMPLATES: ${self:service}-html-templates-sf68N5umh8gC8yM4
    S3_LANGUAGE_TEMPLATES: ${self:service}-language-templates-gY9b7REadVPtKChV
    S3_STATIC_WEBSITE: '${self:service}-static-website-pD4c7M2297pjAmST'

functions:
  send:
    handler: scores/producer.send
    events:
      - http:
          path: scores
          method: post
          integration: lambda
          cors: true
    iamRoleStatements:
      - Effect: Allow
        Action:
          - "sqs:SendMessage"
          - "sqs:GetQueueUrl"
        Resource:
          Fn::GetAtt: [ MyQueue, Arn ]

  receive:
    handler: scores/consumer.receive
    events:
      - sqs:
          arn:
            Fn::GetAtt:
              - MyQueue
              - Arn
    iamRoleStatements:
      - Effect: Allow
        Action:
          - "s3:GetObject"
        Resource:
          - 'arn:aws:s3:::${self:provider.environment.S3_HTML_TEMPLATES}/*'
          - 'arn:aws:s3:::${self:provider.environment.S3_LANGUAGE_TEMPLATES}/*'
      - Effect: Allow
        Action:
          - "s3:PutObject"
        Resource:
          - 'arn:aws:s3:::${self:provider.environment.S3_STATIC_WEBSITE}/*'

resources:
  Resources:
    MyQueue:
      Type: "AWS::SQS::Queue"
      Properties:
        QueueName: "MyQueue"
    S3HTMLTemplatesBucket:
      Type: "AWS::S3::Bucket"
      Properties:
        BucketName: '${self:provider.environment.S3_HTML_TEMPLATES}'
    S3LanguageTemplatesBucket:
      Type: "AWS::S3::Bucket"
      Properties:
        BucketName: '${self:provider.environment.S3_LANGUAGE_TEMPLATES}'
    S3StaticWebsiteBucket:
      Type: "AWS::S3::Bucket"
      Properties:
        BucketName: '${self:provider.environment.S3_STATIC_WEBSITE}'

I don't know if it can help but I also provided below the links to cloudformation templates that were generated:

create-template

update-template