Adding top to existing pants

[xWolfSpiritCSSx]

So, i don't know if anyone is still around on here. It's been a while since I was on IMVU myself. I am using the classic version as I do not like the new version at all. Anyway, I'm trying to remember how to add my shirt to an existing pants mesh. Now i get the shirt in, think i'm doing it right but then when i hit apply it makes the body go invisible. I'm obviously forgetting something, but for the life of me can't remember what it is. lol anyone around that can help?

Thanks