Hi, it does not "click" into place. If you push down in the center, it should spread out to be a tight bottom, then put the folding layer "shelf" on top. Mine does not buckle up, especially if items are inside the cart. To unfold the cart, simply pull up from the center, and wiggle it around a bit as you lift the cart.

I have same experience - does seem that it should lock but I suspect when weighted it is poobably fine🤞🤞