Create the Application
- Visit https://developer.twitter.com/apps and log in to your Twitter account.
- Click "Create an App"
Fill out all required fields. You can find your callback URL in "Settings > Simple Social Login > Twitter".
Ensure "Allow this application to be used to Sign in with Twitter" is checked.
Once the app has been created click the "Permissions" tab then "Edit". Adjust the permissions to:
Update Callback URL
There is currently an inconsistency between Twitter's old app dashboard and the new developer dashboard (ref). To update the Callback URL to the required URL visit https://apps.twitter.com/ and find the application you just created.
Once there add the full callback URL found in "Settings > Simple Social Login > Twitter".
Configure Plugin Settings
Back in your WordPress dashboard visit "Settings > Simple Social Login > Twitter". Enter the App credentials found in "Keys and tokens" tab in the Twitter application settings.