Login on your LinkedIn account and go to the LinkedIn Developers section.
Press Create Application.
Set Company Name, App description, Application Logo, Privacy policy URL, and Business email.
In Legal Terms, select “I have read and agree to the LinkedIn API Terms of Use.”
Click on Create app to create an application.
Go to OAuth 2.0 and add these Redirect URLs
Press Update button
Copy the Client ID and Client Secret from the Application credentials and paste them into the Social Network Configure tab.

In that case, please get in touch with LinkedIn’s support directly.