To use LinkedIn as a social login provider, you will need a Client ID and Client Secret from your LinkedIn app, then copy those keys into your ReachFive settings.
This docs detail steps by steps how to create a LinkedIn application and connect it to your ReachFive account.
Go to https://developers.linkedin.com, login with your account and go to My Apps menu.
Configure your application
Get your Client Id and Client Secret.
In Authorized Redirect URLs, enter
REACHFIVE_DOMAIN is your ReachFive domain.
You may add staging AND production URL.
Click on Update.
Make your application live
On Settings menu, change your application status to Live and click to update.