What country are you in? 
and what’s the model number of the hub? (It should be on a sticker on the bottom.)
The very first SmartThings hub, the V1 in the US, was discontinued last year and doesn’t work with the SmartThings app any more, old or new architecture. So if you have a never-used one sitting in a box somewhere, you’re out of luck. It won’t work now and it won’t work in the future.
The first hub for the UK was the same as the V2 in the US. It should work fine with these changes.
Here’s the thread that discusses the hardware requirements for the new platform.