You would click on the search function at the top right of your screen and enter “crypto paywall”. This would give you this as the first answer: Unlock Discourse plugin: Lock topics behind a "crypto" paywall
It is a solution working with NFTs which can have a time limit. Look it up.
@spirobel also worked on a version of Discourse subscriptions but with Monero, which is amazing!
I didn’t try it myself yet and it’s admittedly a bit harder to find. Here it is: GitHub - spirobel/monero-discourse-subscriptions: A Discourse plugin that allows payments and subscription management via Monero.