Setting up Twitter Connect (from version 4.9.24)

Go to https://apps.twitter.com/ and press Create New App
Enter Name, Description, Website fields. In the Callback URLs field enter your website address and add ?upslug=twitter at the end. Press Add a Callback URL and Create your Twitter application.
Go to Keys and Access Tokens and copy Consumer Key and Consumer Secret keys.
Go to WordPress dashboard UserPro->Settings->Twitter Integration, set Allow Twitter Social Connect to Yes and paste those keys. In the Custom Redirect URL After Login setting enter the same address with ?upslug=twitter as in the step 2.
Press Save Changes.
Now you should able to see Twitter login icon in the login page.