The Sims 4 Tray Importer is a very useful application, which can help you find the CC that has been showing up invisible, with question...

Batch Fixing can fix a number of your problems. Is your CC furniture disappearing when you place it? are you getting a “Script call...

Sim 4 Studio is helpful for fixing and managing broken CC and creating your own content.

Mods and CC can come in forms of Rar, ZIP, and 7z files. These need to be extracted in order for them to work in your game. Use 7-Zip!