How to I add APPLY with LINKEDIN

The problem you're encountering is that the Joomla Email Cloaking plugin is obscuring the email address causing the tag to not be read correctly by JFBConnect.

For the Content plugin, automatically adding the Apply button, we have a fix already implemented in the code. If you're adding the tag by itself, you should also add the following tag which will disable email cloaking as well: {emailcloak off}. The alternative is to disable the email cloaking plugin altogether.

Hope that helps,
Alex