"Project Key" needs to be replaced with "Script ID"

[rubenflamshepherd]

As a heads up to others, "Project Key" is deprecated. Use "Script ID" instead.

This can be found from the "Script Editor" GUI > File > Project Properties and must be used instead of the "Project Key" in the callback url (https://script.google.com/macros/d/YOUR_PROJECT_KEY/usercallback) otherwise you'll get a Invalid redirect_uri parameter value error.

Would submit a pull request but it appears this project is no longer being maintained.

[simonbromberg]

If you submit a PR I would review / merge it