I try to use my subclass but:

screenshot

"This homebrew Subclass does not have the necessary class features with the correct required levels."

I wish it would just tell me which features I need to create, though.

I'm just trying to create a PC version of a doppelganger creature. My link: https://www.dndbeyond.com/subclasses/476137-doppelganger

You don’t need to publish it to use it. In fact, I would recommend against publishing if you’re not even sure what levels you need. Not to mention, a Dopleganager would be better as a race than a class.

Yes, I just figured this out myself and added all of the features from the class into the race. Thank you!