Unable to Make 2014 Rogue Assassin

I'm trying to make an Assassin with the 2014 PH, and in the character creation tab, I have the "2014 Core Rules" box checked.  But when making my character, Assassin does not show up.  And when I uncheck "Core Rules" I lose the only subclass I had, Thief.

You've selected the 2024 version of the Rogue class. You'll need to remove it and select the 2014 version (the one under "2014 Core Rules", not the one under "Core Rules") instead.

(The "2014 Core Rules" checkbox is just a filter that controls which character options are displayed. It doesn't change which ones you already have selected.)

Piggybacking this post as opposed to starting a new one. I have tried all variations but can't get the Assassin subclass at third level. 

I've tried 2024 and 2014 checked, 2024 only and 2014 only - but it won't show. Any further advice would be gratefully received

Quote from Fluffovercrunch >>

Piggybacking this post as opposed to starting a new one. I have tried all variations but can't get the Assassin subclass at third level. 

I've tried 2024 and 2014 checked, 2024 only and 2014 only - but it won't show. Any further advice would be gratefully received

Which version do you want to use? Do you own the book that that version comes from (the Player's Handbook for that version of the rules)?

That's the problem I overlooked. I didn't realise I needed to own the DnD Beyond Player's Handbook in order to use the subclass. 

Many thanks for helping me out - much appreciated

Quote from Fluffovercrunch >>

That's the problem I overlooked. I didn't realise I needed to own the DnD Beyond Player's Handbook in order to use the subclass. 

Many thanks for helping me out - much appreciated

Just to expand on that: everyone on D&D Beyond has access to a free digital book called D&D Beyond Basic Rules that gives you access to the core 12 classes, but only includes one subclass for each of them. For Rogue, it's the Thief subclass.

Every other subclass is associated with a specific source book, so to use it in the character builder you need to either a) purchase the digital version of that book on D&D Beyond, or b) join a D&D Beyond campaign where the book is being shared.