I encountered an issue when googling this problem, most information I found was outdated and referenced the old stop disc.
If you have a newer brompton you have a stop block instead of the old stop disc and you probably will need to adjust this slightly, here's Bromptons own video:
https://www.youtube.com/watch?v=lSYRvL4YSgI
Reddit usually ranks pretty high on google searches, so I hope this helps someone else struggling in my situation 🙂
by the-gorg