I have tried and tried to use homebrew subclasses.   I am even subscribed so I should be able to add a home brew subclass to a character I have created.  I can't figure out what I am doing wrong.  It should be as easy as clicking on the sub-class, adding it to my collection and then adding it to my class.   But it will not add the subclass into my collection that I can see and I am even subscribed.  Do I need to do something else that I am missing?   Can someone please give me some direction.  I have look through all the homebrew tutorials I can find and I still can't figure out what is wrong. 

First check that the subclass has actually been added to Your Homebrew Collection. If it has, then see the General FAQ #5: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq).

I don't know what I am doing wrong.  I have tried to add one of your monk sub classes but there is no way to add a subclass in any one of my screens  I have the subclass in my homebrew collections but when I try to add it there is not a prompt or a button or anything to actually add the subclass.   I have even read through all the FAQs.  Nothing seems to work.  Can you make any other suggestions?

Is your character 3rd level? Monks get their subclasses at 3rd level.

Well that would explain why I can't see the subclass yet.  So I can't even really add it until 3rd level.  I assume a lot of the other classes are the same .  I wouldn't see it until a higher level.   Is there a list somewhere that I have missed that shows what level each class can add a sub-class?   BTW, thanks loads for the assist.   When I used to play was back in the early 80's.   None of this high tech stuff back then.   

Sorry it took so long, I only just noticed your reply. If I’m not mistaken, Clerics, Sorcerers, and Warlocks get their subclasses @ 1st level, Wizards and Druids get theirs @ 2nd level, everything else gets theirs @ 3rd level.

Thanks   I really appreciate all the information.