Read carefully the Ruby example in your own post here

client = RPCClient.new(
  access_key_id:     '<accessKeyId>',
  access_key_secret: '<accessSecret>',
  endpoint: 'https://dysmsapi.aliyuncs.com',
  api_version: '2017-05-25'
)
[download]

access_key_id and access_key_secret are not the same

poj