title: Heroku error: "key must be 16 bytes" but the key I have inputted is 16 bytes
body: <p>I am launching to Heroku for the first time and I am getting the error "ArgumentError: key must be 16 bytes".  </p>
  
  <p>I have run <code>rails credentials:edit</code> to generate a new key, got the key which is 32 characters, ran <code>heroku config:set RAILS_MASTER_KEY='&lt;master key&gt;'</code> and it was accepted.  But I still get the error when I run it.  </p>
  
  <p>I am unsure what I am doing wrong.</p>
  
  <p>Here is the full error message:  </p>
  
  <pre><code>Running: rake assets:precompile
         rake aborted!
         ActiveSupport::MessageEncryptor::InvalidMessage: ActiveSupport::MessageEncryptor::InvalidMessage
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/message_encryptor.rb:206:in `rescue in _decrypt'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/message_encryptor.rb:183:in `_decrypt'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/message_encryptor.rb:157:in `decrypt_and_verify'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/messages/rotator.rb:21:in `decrypt_and_verify'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_file.rb:79:in `decrypt'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_file.rb:42:in `read'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_configuration.rb:21:in `read'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_configuration.rb:33:in `config'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_configuration.rb:38:in `options'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/core_ext/module/delegation.rb:271:in `method_missing'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/devise-4.6.2/lib/devise/secret_key_finder.rb:24:in `key_exists?'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/devise-4.6.2/lib/devise/secret_key_finder.rb:10:in `find'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/devise-4.6.2/lib/devise/rails.rb:37:in `block in &lt;class:Engine&gt;'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `instance_exec'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `run'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:61:in `block in run_initializers'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:60:in `run_initializers'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:361:in `initialize!'
         /tmp/build_e151bdf198daf12c42102939c20b0959/config/environment.rb:7:in `&lt;top (required)&gt;'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `block in require_with_bootsnap_lfi'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require_with_bootsnap_lfi'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in `require'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `block in require'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:257:in `load_dependency'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `require'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:337:in `require_environment!'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:520:in `block in run_tasks_blocks'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/sprockets-rails-3.2.1/lib/sprockets/rails/task.rb:62:in `block (2 levels) in define'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/rake-12.3.2/exe/rake:27:in `&lt;top (required)&gt;'
  
         Caused by:
         ArgumentError: key must be 16 bytes
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/message_encryptor.rb:193:in `key='
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/message_encryptor.rb:193:in `_decrypt'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/message_encryptor.rb:157:in `decrypt_and_verify'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/messages/rotator.rb:21:in `decrypt_and_verify'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_file.rb:79:in `decrypt'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_file.rb:42:in `read'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_configuration.rb:21:in `read'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_configuration.rb:33:in `config'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/encrypted_configuration.rb:38:in `options'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/core_ext/module/delegation.rb:271:in `method_missing'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/devise-4.6.2/lib/devise/secret_key_finder.rb:24:in `key_exists?'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/devise-4.6.2/lib/devise/secret_key_finder.rb:10:in `find'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/devise-4.6.2/lib/devise/rails.rb:37:in `block in &lt;class:Engine&gt;'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `instance_exec'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `run'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:61:in `block in run_initializers'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/initializable.rb:60:in `run_initializers'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:361:in `initialize!'
         /tmp/build_e151bdf198daf12c42102939c20b0959/config/environment.rb:7:in `&lt;top (required)&gt;'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `block in require_with_bootsnap_lfi'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require_with_bootsnap_lfi'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.4.4/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in `require'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `block in require'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:257:in `load_dependency'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `require'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:337:in `require_environment!'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/railties-5.2.3/lib/rails/application.rb:520:in `block in run_tasks_blocks'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/sprockets-rails-3.2.1/lib/sprockets/rails/task.rb:62:in `block (2 levels) in define'
         /tmp/build_e151bdf198daf12c42102939c20b0959/vendor/bundle/ruby/2.5.0/gems/rake-12.3.2/exe/rake:27:in `&lt;top (required)&gt;'
         Tasks: TOP =&gt; environment
         (See full trace by running task with --trace)
   !
   !     Precompiling assets failed.
   !
   !     Push rejected, failed to compile Ruby app.
   !     Push failed
  </code></pre>