Trouble creating new facial hair

Hi, I want to combine two facial hair options that are already in the game (soul patch and handlebar moustache). I followed some tutorials, I joined both meshes in Blender and saved it but when I try to import the new mesh in The Sims4 Studio, the moustache part looks weird, without any texture. The tutorials I saw did the same thing but with hairstyles, and they didn't have this issue...is that a facial hair thing?

Can please someone help me? I'm a total noob with this kind of things but I cannot find this facial hair option anywhere and wanted to create it myself...