Why I am getting Could not find multi_json-1.3.1 in any of the sources?

Question

I have a simple Rails application I want to deploy to Heroku. When I run the below command

git push heroku master

The below error message is di

Answer 1

In my case, I was lacking

source 'https://rubygems.org'

in Gemfile. My suspicion is that old versions of bundler can operate without a source being mentioned, but newer versions can't.