Space Key Only Works When Pressed In The Center

It's not fully attached all the way.. There is usually, depending on the style and type of keyboard a metal like bard that clips on the key as well connects to the board, sometimes when you're putting the back on it doesn't fully set and you either have to push the key down pretty hard to make sure the clips make contact OR take the bar out and attach it to the key first and then set the key back down in place on the board and again you might have to push kinda hard so those clips can well clip lol.

Hope this helps.