My add-on doesn't show up in game
Check three things: the folder is the Forever one, not retail or Classic (see the install guide); the add-on folder isn't nested inside another folder of the same name; and you restarted the game after copying it.
It shows as "out of date"
The add-on has no Forever build yet, or the author hasn't updated its version number. Check its page here for the status. If you load it anyway, keep BugSack running.
I get Lua errors every fight
Install BugSack and BugGrabber, reproduce the error once, and look at which add-on it names. Disable that one first. More: catching Lua errors.
My settings disappeared
Settings live in the WTF folder. Restore from a backup, or see backing up add-on settings.
Can I use my beta UI on live
Usually yes, by copying the add-on folders and WTF settings. Steps: move your beta UI to live.
Which download is the real one
Only the author's official page: CurseForge, Wago or their GitHub. Every add-on page here links there and nowhere else.