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.
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.
On Settings menu, change your application status to Live and click to update.