u/I_Sell_Onions

So, I have 2 kallax units both the 2x4 models. One I built myself and the other I bought used online and it came with 2 (4) drawer attachments and 2 doors already installed. So the one I had laying horizontally I moved into my room and turned it vertically and put in on the small kallax underframe. No problem.

Now I'm trying to finish assembling the large kallax underframe and just need to secure the hex screw with the white "wheel" to the bottom of the kallax itself but it's just not going in and lot letting me attach it. What Im I doing wrong???