Review this article and get a short FaceBook link/URL:

https://support.teamsideline.com/hc/en-us/articles/201151907-How-to-get-a-short-Facebook-user-name-Facebook-link-not-long-enough

Next step is to go to the Content > Configurations > General page and add the URL to the Facebook URL field under the Site Social Links section.  Your FaceBook link will now appear on the bottom of all of your public website pages and your organization's email communications.