Addon problems PLEASE PLEASE PLEASE HELP

I download addons and put them into the correct folders/addons folder. And they never show up in the game! Please can someone help me? For example I put PHX into the addons folder and the list showed up in game but w/e I spawn anything it just shows up as an error! I’m able to get maps and whatnot but addons never work!

Did you restart gmod after installing it?

Are you using a pirated version of Gmod?

Some addons are required to be put in different folders. Try putting the models in the /models folder. This may or may not work. The code may be set to searching the /models folder for the picture or skin of the object.

Slight mistake, addons always go into the addons folder.
You may have put a non addon format folder into the addons folder, check if any of the addons have info.txt in them. If they don’t, they’re not addons.