If you make an API call using an invalid token, you will receive a "401 Unauthorized" response back from the server.
An expired access token. Generated access tokens have a lifespan of only 60 days.
The user might have revoked the permission they initially granted to your application.
You have changed the member permissions (scope) your application is requesting.
To resolve the issue, you have to refresh the LinkedIn connection and ask the user to authorize your application for access the LinkedIn profile instance used in the integration.