According to the composer.json of that module, you need happyr/linkedin-api-client
. So to install that with Composer, from the root of your Drupal project run:
composer require happyr/linkedin-api-client:1.0.0
composer require happyr/linkedin-api-client:1.0.0
Since that library has dependencies too, you probably need to install them too. Basing on the documentation, you could need to execute the following too.
composer require php-http/guzzle6-adapter
composer require guzzlehttp/psr7 php-http/message