Heroku uses the referrer URL to point at the repo that should be deployed; from this page that includes part of a path that breaks the deployment (specifically /blob/master/docs/Running-Mastodon/Heroku-guide.md). I've replaced the vanilla address with one that includes a specific reference to the root of the repo
Index
Mastodon is a free, open-source GNU social-compatible social network server. A decentralized alternative to commercial platforms, it avoids the risks of a single company monopolizing your communication. Anyone can run Mastodon and participate in the social network seamlessly.
Using Mastodon
Using the API
- API documentation
 - Streaming API documentation
 - Testing the API with cURL
 - OAuth details
 - Tips for app developers
 - Push notifications
 
Running Mastodon
- Production guide
 - Alternative: Running on Heroku
 - Development guide
 - Alternative: Development with Vagrant
 - Administration guide