How to create a Linkedin Application:

Please go at this url https://www.linkedin.com/secure/developer
and click on 'Create Application'.

Fill in the required informations.
For 'Application Logo URL' you can enter a placeholder such as: https://localhost
Same for 'Website URL' you can enter : http://localhost
Click 'Submit'.

On the 'Authentication' tab.
Copy the 'API Key' and 'Secret Key'
(you'll need them when creating your linkedin account in MicroblogPoster).

Still on the 'Authentication' tab.
For 'OAuth 2.0 Redirect URLs', enter the Url such as: (Linkedin has made that field mandatory recently.)
http://your-blog-url/wp-admin/options-general.php?page=microblogposter.php
Leave everything else by default.
Click 'Add' + Click 'Update'.

On the 'Settings' tab.
For 'Live Status', select Live.
Click 'Update' at the bottom.

Configure your linkedin account in the Social Accounts section.

Follow the link provided by MicroblogPoster to authorize your App posting on your behalf.