Here are steps for integrating Keenicons in a Ruby on Rails application and resolving the fonts issue in a production environment like Heroku:

1. Move the Keenicons assets to your application's asset folder by placing them in the app/assets/fonts directory.
2. Load the fonts in the asset pipeline by adding the following line to your config/application.rb file:
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   config.assets.paths << Rails.root.join("app", "assets", "fonts")

3. Move the style.css files for each Keenicon variant (e.g., fonts_duotone_style.css, fonts_outline_style.css, "fonts_solid_style.css) to the app/assets/stylesheets directory.
4. Rename the style.css files to style.scss.
5. In the style.scss files, update any references to font URLs using the font-url helper provided by Rails. For example, change:
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   url('fonts/keen-icons.ttf') format('truetype');

   to:
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   font-url('keen-icons.ttf') format('truetype');

6. Include the Keenicons styles in your application's stylesheet by importing the "style.scss" files. You can do this by adding the following line to your main stylesheet file (e.g., "application.scss"):
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   @import 'style';

7. If you're using the Asset Pipeline, precompile the assets by running the following command:
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   RAILS_ENV=production bundle exec rake assets:precompile

8. Deploy your application to the production environment, such as Heroku, ensuring that the precompiled assets are included in the deployment.

By following these steps, you should be able to integrate Keenicons into your Ruby on Rails application and resolve any font-related issues.