You now have "an f-code".
At the bottom of each thread in the digital market forum that is selling something, you should see a box offering your affiliate link.
If the regular thread URL is:
https://permies.com/t/99999/delicious-fishes-the-movie
And your f-code is 7 (that's actually my f-code). Then this would work:
https://permies.com/t/99999f7/delicious-fishes-the-movie
and this would also work:
https://permies.com/t/99999f7
And the description part is largely ignored in finding the thread - and the proper name will be used once you go to the thread, so you can fiddle with it all you want:
https://permies.com/t/99999f7/delicious-fishes
https://permies.com/t/99999f7/delicious-fishes-movie
https://permies.com/t/99999f7/fishes
https://permies.com/t/99999f7/delicious-fishes-in-ma-belly
If somebody follows a link to permies with your affiliate code, that code is stuck into a cookie in their browser for 7 days, and if they buy anything, you get the affiliate cut. Of course, somebody else's affiliate code could overwrite yours, the user can wipe their cookies .... it is a cruel world out there for cookies, but it will probably survive most of the time.