How to Establish a LinkedIn Connection

Help. Several months ago, I successfully established an API connection to LinkedIn and have been using Make to submit a daily post since - it works great. Now, I’m trying to build a scenario for a customer to provide the same service, and I’m struggling with the connection. Since I cannot see the details of my original connection, I’m starting over. Below are the connection fields and content:

Connection Type: LindedIn
Connection Name: SCA-Post
Client ID: 14characters which is found on the developer.linkedin site under My Apps
Client Secret: Also found on the developer.linkedin site under My Apps
Developer Application URN: urn:li:organization:999999999 (9-digit number)

I’m trying to set this up the same way I did previously, but I’m missing something.

I’ve looked thru a number of posts on this site but have not yet found anything to solve the problem. So I apologize if I’ve missed it. Thanks in advance for your help! Eric