What exactly isn't working? I'm guessing you don't have a category with the correct 'sef'.

If this is your route: 'maincat/cat2/cat3/item', then it'll assume $cat4 is item so do you have a category where 'sef' is equal to 'item'?

yeah laravel wouldnt know how to differentitate category/item you give in url e.g

url.com/category1/item or url.com/category1/category2....

to laravel they look the same.. so you probably need to change the way you are serving either by adding another hardcoded stuff so like:

url.com/category/men/item/clothes << item is hardcoded.. which you can then use routing

but to be honest when you are showing ITEMS you shouldnt have something like url.com/category1/category2/categroy3/item..

just do url.com/items/itemid

and then on the items you can have a breadcrumb showing you how the item is located on yoru site..