Self-hosted, working YOURLS install... I have used this plugin in previous versions of WordPress... plenty of experience authenticating plugins/apps with Twitter, etc.
Received the error "Could not authenticate you" in Twitter section of plugin settings. Logging in with Twitter via button does not correct the problem. No other indication of problem except:
1. Plugin requires Twitter API to be set to "Browser," but that was not an option when I created this Twitter app.
2. There is no entry after "Set Callback URL to" .