Hi Laurie,
To find your Facebook’s page URL just visit your page and check the ending of your Facebook page URL in your browser’s address bar.

Make sure you’re adding a Facebook URL that links with a Facebook business/fan page and not a personal profile, that can only be viewed by your friends.
You can read here what are the differences between a Facebook page and a Facebook profile: https://www.socialstorepro.org/what-are-the-differences-between-a-facebook-page-and-a-facebook-profile/
Sincerely,
- Tzipi