The first thing to do is to make sure you're using LinkedIn + Powerin + Chrome extension in the same Chrome session.

This has to be done on Chrome, not Brave, Opera or other browsers, which will create interference and problems that won't let Powerin run at 100% of its capacity.

If you use all the elements in the same session. Understand that you cannot add a LinkedIn to a new Powerin account. So if you've already added a LinkedIn to a Powerin account, you can't add it to another account. 

If you wish to do so, please contact support with the following information: 
1. LinkedIn profile URL
2. Old account e-mail

If it still doesn't work and you can't connect you're LinkedIn, contact support with your LinkedIn URL Profile too.