I had the same problem with it always coming back to the login screen on https://labs.geocaching.com/builder/adventures. After driving around the site for a bit, I found this page: https://www.geocaching.com/play/request/adventurelab. That's where you Opt-in to the offer, and they'll notify you in a few months if you qualify and then you get the credit. Then the original link will probably work as intended.
Updated May 10: they fixed the bug causing what I experienced above. The https://labs.geocaching.com/builder/adventures link now takes me to a page that shows my credit.
@Corp Of Discovery, yes you may still need to qualify in other ways. But for anyone that was stuck on the login screen before, give it a try now.