Kakao Connect
To use KakaoTalk as a social login provider, you will need an App ID and App Secret from your Kakao app, then copy these keys into your ReachFive settings.
This docs detail steps by steps how to create a Kakao App and connect it to your ReachFive account.
Developer access
Go to https://developers.kakao.com and log in
Note: If you do not have a Kakao account with a registered email address, go to https://accounts.kakao.com/ and click "sign up"

Log-in with your account. Check the two boxes (Acceptance of service use policy and consent to the collection and use of personal information policy)

Fill the requested field with your email, your name and a company name:

Click on "register"
Set data parameters
Click on "User management" in the left-hand menu

Switch the button to "On" position.

It displays data you can request to collect when a user logs in. Set all the permissions to the second column "Choose at sign in". It means to permissions will be asked to your user, they can choose to give it or not. You have to explain why you need those permissions.

Click on "Save"

Configure your application
Go on the "Client Secret" menu

Go on your App homepage by clicking on the name of your app in the left-handed menu

Go on "Settings"

Click on "Add a platform"

Select Web Platform.
Add https://{REACHFIVE_DOMAIN}/login/callback
as Callback URL, where REACHFIVE_DOMAIN
is your ReachFive domain.
You can add your Production ReachFive domain and your staging ReachFive domain
Then click on "Save"

Enter the following path in Redirect Path : login/callback and click on Save

Configure KakaoTalk as provider on ReachFive
Go on your App homepage by clicking on the name of your app in the left-handed menu

Click on "See the API keys" and paste the REST key

Go to the ReachFive Console. Go to Settings > Providers.
Click on KakaoTalk
Paste your REST API Key in Client ID

Click on "Save"
On KakaoDevelopers, go to "Client Secret"

Paste your Client Secret.
Switch the button to "On" and click "Save" alongside.

Go to ReachFive Console. Go to Settings > Providers. Click on KakaoTalk
Paste your Client Secret in Client Secret

Switch to "visible" and click "Save"