To integrate your Facebook App with your marketplace, follow these steps:
Go to https://developers.facebook.com/ and log in.
Open the app you created via the "Apps" drop-down in the upper-left corner.
In the left-hand menu, select "Apps settings" and then "Basic”.
Note the "App ID" & “App Secret,” a long chain of characters, from this section
Log in to your marketplace as an administrator.
Navigate to the "Social Media" page in your Admin panel.
Locate the "Facebook sign-in" section.
Enter the "App ID" you noted earlier into the "Facebook App ID" field
Enter the “App Secret” you noted earlier into the “Facebook App Secret” field
Click "Save settings”.
Your Facebook Login is now active and configured in your marketplace, allowing users to create accounts or log in using their Facebook credentials. Take some additional time to customize your app on Facebook as desired.