You can take an API key and encryption phrase from the Site manager:
As I heard the next (maybe alpha?) version of FileZilla should have an ability to create a shareable URL right from the UI, but I have no details yet.
Also, I think the generated URL could be useless, because you likely will not see an error if download file via linkshare.
Maybe you should give an access grant instead. In the last case I would recommend to limit it by time: https://documentation.tardigrade.io/getting-started/sharing-your-first-object/share-a-restricted-access-to-an-object