It's important to note that the prompt displayed above will only work if you have a Facebook Page connected to your site - NOT a Facebook Group.
The difference between the two may seem subtle, but connecting the URL of a Facebook Group to your LeagueApps site will actually cause problems with your site's Facebook integration - most notably a 'phantom prompt' where users will essentially be stuck in the middle of registration because the prompt to 'like' your Facebook page has no content or links:
Here's a little more on the differences between a Facebook Page and a Facebook Group and why Facebook Pages are a part of the integration with LeagueApps:
Facebook Pages are public, can be found through search, and anyone can 'like' the page. You can limit a page to being visible in certain countries, and to some extent certain ages only, but overall a Facebook Page is meant to be an official representation of an organization on Facebook. Think of your organization as a brand, and creating a Facebook Page for your organization allows you to post messages and content to your followers (people who like your page) as the official brand. You can add your organization's logo, description, contact info and anything else you want to show the world about your organization.
Facebook Groups can be public, closed (anyone can find Group, only members see posts) or secret (nobody can find the Group unless added by a member). Facebook Groups are good for organizing on a personal level and to communicate with people on a smaller scale. Think of a Facebook Group as a big message board or forum where the members are the ones posting messages and content. They're useful, just not when it comes to your LeagueApps site's Facebook integration.
Facebook Pages are the only way to go with your LeagueApps Facebook integration and they're overall a much better resource for businesses, organizations and brands. To create a Facebook Page go here: https://www.facebook.com/pages/create/