How to resolve permissions error when setting up ChatOps?

Issue

I am the owner of the Github Org/Repo and Heroku. When trying to use ChatOps to deploy, I get the following error.

Unable to access XXX
Please make sure you have access to this GitHub repository. Read more about permissions and try to sign in to GitHub again.

Resolution

Please follow this instruction: https://devcenter.heroku.com/articles/chatops#why-do-i-get-this-please-make-sure-you-have-access-to-this-github-repository-error