"bundler: failed to load command: thin" on Heroku - ruby-on-rails

Question

I'm using Ruby 2.2.7, and Rails 3.2.21, and trying to deploy an with gem: locomotive_cms of version: ~> 2.5.7 on Heroku, and it gets deployed successfully, but I'm facing the following error:
2017-08-12T23:33:13.732440+00:00 app[web.1]: bundler: failed to load command: thin (/app/vendor/bundle/ruby/2.2.0/bin/thin)
2017-08-12T23:33:13.732490+00:00 app[web.1]: /app/vendor/bundle/ruby/2.2.0/gems/excon-0.23.0/lib/excon/middlewares/expects.rb:6:in `response_call'
And with that, it produces this too:
Heroku::API::Errors::ErrorWithResponse: Expected(200) <=> Actual(400 Bad Request)
I have thin in my Gemfile which is necessary for locomotivecms according to its documentation.
I have been on other similar questions too, but I'm still unable to solve my problem. I have Ruby version: 2.2.7, and while it is saying: /app/vendor/bundle/ruby/2.2.0/bin/thin
Gemfile:
source 'https://rubygems.org'
ruby "2.2.7"
gem 'rails', '3.2.21'
# Bundle edge Rails instead:
# gem 'rails', :git => 'git://github.com/rails/rails.git'
gem 'locomotive_cms', '~> 2.5.7', :require => 'locomotive/engine'
gem 'dotenv-rails'
gem 'savon', '~> 2.3.0' # SOAP client for pulling in events
gem 'twitter', '5.8.0'
gem 'twitter-text'
gem 'whenever', require: false
# Gems used only for assets and not required
# in production environments by default.
group :assets do
gem 'compass-rails', '~> 2.0.0'
gem 'sass-rails', '~> 3.2.4'
gem 'coffee-rails', '~> 3.2.2'
# See https://github.com/sstephenson/execjs#readme for more supported runtimes
gem 'therubyracer', :platforms => :ruby
gem 'uglifier', '~> 1.2.4'
end
group :development do
gem 'unicorn'
gem 'pry'
end
# To use ActiveModel has_secure_password
# gem 'bcrypt-ruby', '~> 3.0.0'
# To use Jbuilder templates for JSON
# gem 'jbuilder'
# Use unicorn as the app server
# gem 'unicorn'
# Deploy with Capistrano
# gem 'capistrano'
# To use debugger
# gem 'debugger'
# To use on Heorku
gem 'locomotive-heroku', '~> 0.1.0', :require => 'locomotive/heroku'
gem 'thin'
Gemfile.lock:
You can find it here: https://gist.github.com/Arslan-Ali-Butt/640c1ec1750d17c9803e12a492f35c4e

Answer 1

Sorry in advance for the bad news.
I've taking a look at your Gemfile and Gemfile.lock, and also at the PR https://github.com/locomotivecms/locomotive-heroku/pull/11 and the latest 2.5.x branch of locomotive_cms at https://github.com/locomotivecms/engine/tree/v2.5.x. You've reached the end of functionality due to the lack of maintenance on the versions of the Gems that you depend on.
locomotive_cms has been renamed to locomotivecms and bumped to version 3+. The locomotive_cms gem is no longer maintained. Not only that, but it's no longer compatible with a bunch of the other dependencies you're using, namely excon.
Bundler could not find compatible versions for gem "excon":
In Gemfile:
locomotive_cms was resolved to 2.5.8, which depends on
fog (~> 1.12.1) was resolved to 1.12.1, which depends on
excon (~> 0.23.0)
locomotive-heroku was resolved to 0.1.0, which depends on
heroku-api (~> 0.3.23) was resolved to 0.3.23, which depends on
excon (~> 0.44)
You're going to want to go through the upgrade guide at https://locomotive-v3.readme.io/docs/upgrade-to-v3.

Answer 2

Add a Procfile (place a file named Procfile in the root of your app), to tell Heroku to use thin, like so:
web: bundle exec thin start -p $PORT
That will allow you to run thin in production on Heroku. I assume that your Gemfile is properly configured
The second message points to a bad request according to Heroku API guide, but it's hard to tell how it is connected to the first error message.