Authenticating Your Twitter Account with Twitterrific (iOS and macOS)

Why am I sent to an authentication webpage when adding a new Twitter account in Twitterrific?

Twitter requires third-party applications re-authenticate themselves for access to direct messages. In order for Twitterrific to send and receive DMs, Twitter requires that you approve access for the app using their OAuth webpage. Once you allow access there, you'll be taken back to Twitterrific.