“This website is free” no longer applies.

The payment feature, called Super Follows, will allow Twitter users to charge followers and give them access to extra content. That could be bonus tweets, access to a community group, subscription to a newsletter, or a badge indicating your support. In a mockup screenshot, Twitter showed an example where a user charges $4.99 per month to receive a series of perks. Twitter sees it as a way to let creators and publishers get paid directly by their fans.

Source: Twitter announces paid Super Follows to let you charge for tweets – The Verge