In my Rails API I have this code in cors.rb

Rails.application.config.middleware.insert_before 0, Rack::Cors do
  allow do
    origins 'example.com', 'api_dot_example.com'

    resource '*',
             headers: :any,
             methods: %i[get post put patch delete options head],
         expose: [:Authorization, 'Access-Control-Allow-Origin']
  end
end

In the production.rb I try to define mailer setting like:

config.action_mailer.smtp_settings = {
    ssl: true,
    address: Rails.application.credentials.mail['address'],
    port: Rails.application.credentials.mail['port'],
    domain: Rails.application.credentials.mail['domain'],
    authentication: :login,
    user_name: Rails.application.credentials.mail['user_name'],
    password: Rails.application.credentials.mail['password']
  }

  # config.action_mailer.smtp_settings = {
  #   ssl: true,
  #   address: 'example.com',
  #   port: 465,
  #   domain: 'example.com',
  #   authentication: :login,
  #   user_name: '[email protected]',
  #   password: 'fake_pass'
  # }

When I hard-code the settings (like the comments in the code above), everything works. But if I try to retrieve the setting from rails credentials I get a CORS ERRORS:

OPTIONS api_dot_example_dot_com/login CORS Missing Allow Origin

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at api_dot_example_dot_com/login. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 500.

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at api_dot_example_dot_com/login. (Reason: CORS request did not succeed). Status code: (null).

Can anyone please explain why this is happening?