I got to the point where I'm ready to Deploy to Heroku

After typing git push heroku master I get:

...
remote: Bundle completed (20.59s)
remote: Cleaning up the bundler cache.
remote: -----> Installing node-v16.13.1-linux-x64
remote: -----> Detecting rake tasks
remote:
remote: !
remote: ! Could not detect rake tasks
remote: ! ensure you can run $ bundle exec rake -P against your app
remote: ! and using the production group of your Gemfile.
remote: ! rake aborted!
remote: ! NoMethodError: undefined method new' for BigDecimal:Class remote: ! /tmp/build_d07b8e5c/vendor/bundle/ruby/2.7.0/gems/activesupport-4.2.11.3/lib/active_support/core_ext/object/duplicable.rb:111:in class:BigDecimal'
...

I can run bundle exec rake -P manually but there is a warning:

codio@sigma-speed:~/workspace/rottenpotatoes$ bundle exec rake -P
/home/codio/.rvm/gems/ruby-2.6.6/gems/activesupport-4.2.11.3/lib/active_support/core_ext/object/duplicable.rb:111: warning: BigDecimal.new is deprecated; use BigDecimal() method instead.
rake about
environment
rake assets:clean
environment
...

Anyway, I believe the warning is irrelevant. Otoh, these solutions on StackOverflow might be worth trying.

Regards