It was just pushed up against it. The old dryer had a small piece of duct attached that fit inside This piece. Never knew they put it together like that until i moved the broken dryer!

There is no lip on this vent where i can attach the flexible duct. i purchased a piece i can insert into the floor duct but theres no way to attach it permanentl?!

You'll need to find a solid duct piece to put on the dryer outlet that will fit into the housing, although there may be some air leakage. It presumably originally had a flange on the opening, which apparently was cut off to make room for your tight-fit closet. A reason why washers and dryers shouldn't be installed in such locations.

Thanks so much! I suspected it was missing something as I’d seen the photo you posted too and I couldn’t find any small attachment that fit tightly. I may see if i can replace the whole piece as i now have stackables and took the bifold doors off So theres more room. Not sure if that may be too difficult to do without cutting some sheetrock though!. Ugh! Thanks again!

This won't solve your problem, but once you get the outside piece replaced, you may want to try this product:
Magvent

It was suggested by someone on another forum here.