Setting up Twitter Connect (from version 4.9.39)

Go to https://developer.twitter.com/en/portal/dashboard and press Create New App
Choose planned use for Your application, fill in required fields, that ask about how this application will be used, accept to terms and conditions of the twitter.
Once You’re done, You want to return to this page: https://developer.twitter.com/en/portal/dashboard
In “Projects & Apps” click “Overview” and create new project by clicking “+ New Project” button, fill in name of the project and Your application.
Once You’re finished, You should have such view:
Scroll down and find in Your 3-legged OAuth and edit it
Enable 3-legged OAuth, enable Request email address from users, fill in Callback URL, which is Your website address with /wp-content/plugins/userpro/lib/twitterauth/auth.php at the end, add Website URL, terms and conditions, privacy policy pages and save changes.
Switch to “Keys and tokens” tab, click “View Keys” in API key & secret field
You will see Consumer Key and Consumer Secret keys. Make sure to keep this page in a different tab as You will need it in the next step to copy&paste it.
Return to Your website: Admin dashboard->UserPro->Near the bottom of the page, there will be an expandable tab: “Twitter Integration“
“Allow Twitter Social Connect” set it to “yes”, field “Consumer key, Consumer secret” – look up previous step, copy&paste secret to secret field and key to the key field, Custom Redirect URL After Login – should be identical to step #7 – “Callback URL“
Press Save Changes.
Now you should able to see Twitter login icon in the login page.