Redistogo and Sidekiq on Heroku: Can't connect

Question

I had huge issues with starting sidekiq on Heroku after updating my gems and putting everything into production. The problem was that Sidekiq tried to connect to Redis on a local connection and port, instead of using the REDISTOGO variable. After spending a few hours, I managed to fix it: Answer below.

Answer 1

Not an answer - but want to add to the SEO for this post so others can find this. This is also the answer to an issue where heroku will throw the error:

could not connect to server: No such file or directory
    Is the server running locally and accepting
    connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

This issue has been unanswered on many SO questions (example), and everyone says the database isn't correctly configured, which is not necessarily the case.

I tried for hourrrrsss to figure out the issue, and this was the solution! Thank you so much - I wish I could upvote your answers more than once!!