[Ruby on Rails Final Project] Failed to deploy to Heroku

https://www.codecademy.com/courses/learn-rails/projects/learn-rails_portfolio
Currently I’m on that exercise to create portfolio site. There is a step to deploy the app to Heroku (from local). I’ve followed the instruction from here: https://www.codecademy.com/articles/deploy-rails-to-heroku. But I keep getting the same error message: Precompiling assets failed. Anyone successfully deployed it to Heroku? Is there any solution to fix this problem?