I'm not sure where you've been going to share the URL, but you can perhaps check whether you've set up a Custom Link (as this could make it easier to share). Go to the Listings tab, click your listing and scroll all the way to the bottom to see the Custom Link section.
Could you tell us more about where you've been checking to find your URL please?
In complement to Shelley's suggestion, here's the full help centre article on Creating a custom link for your listing, should you want to read more about this option.