Every time I try to make a subclass, It always says "This homebrew Subclass does not have the necessary class features with the correct required levels."

What are the necessary class features?

It varies by class. Best suggestion when making a homebrew subclass is to use the subclass available for free from the Basic Rules as a template -- it'll have the required features at the required levels, and you just edit the features but not the levels, and add any additional ones you want.

Note Druids are especially weird because the Basic Rules class, Circle of the Land, is the only subclass to get a level 3 feature. So it's set the template for requirements, so all druids must have a level 3 feature, even if it's a blank buffer feature that doesn't show up in the character sheet/editor.

Its a paladin

Please see the General Homebrew FAQ #Ω-1 for the answers to your question: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq).

Fixed!