so i've recently made my first homebrew (can't publish because of incorrect features but thats not the problem) but i can't add it to a character of of my PC's are using, i was wondering if it's because their character is already a roughe and that's causing it to not work

What class is it for and what level is the character? Also, is homebrew enabled for the character?

the class it's for is rogue, i have homebrew enabled and the character is lv 1

Rogues don’t choose their subclass until 3rd level.

that makes sense, i'll wait until their level 3 and try again, thanks for the help