RAILS_MASTER_KEY error on Heroku deployment

Question

I am getting the following error while deploying my rails app on Heroku

-----> Installing node-v8.10.0-linux-x64
-----> Detecting rake tasks
-----> Preparing app for Rails asset pipeline
       Running: rake assets:precompile
       rake aborted!
       Rails::Secrets::MissingKeyError: Missing encryption key to decrypt secrets with. Ask your team for your master key and put it in ENV["RAILS_MASTER_KEY"]

Now if I set environment variable RAILS_MASTER_KEY with the value generated from rake secret . I get this error

-----> Installing node-v8.10.0-linux-x64
-----> Detecting rake tasks
-----> Preparing app for Rails asset pipeline
       Running: rake assets:precompile
       rake aborted!
       ActiveSupport::MessageEncryptor::InvalidMessage: ActiveSupport::MessageEncryptor::InvalidMessage

There is a solution on git regarding this.

https://gist.github.com/kaspth/bc37989c2f39a5642112f28b1d93f343

If I implement the method mentioned in the above github issue. I get the the following error that is also regarding the RAILS_MASTER_KEY.

Generating a new higher entropy encryption key in config/secrets.yml.key.
Rotate the encryption key now.
C:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/railties-5.1.6/lib/rails/secrets.rb:77:in `handle_missing_key': Missing encryption key to decrypt secrets with. Ask your team for your master key and put it in ENV["RAILS_MASTER_KEY"]
(Rails::Secrets::MissingKeyError)

Answer 1

RAILS_MASTER_KEY should contain the same value that is in the file config/secrets.yml.key in your project on your computer. You only need to copy it from the file and paste it in Heroku settings. You do not need to generate new secret.