The issue is caused by the fact our account at WordPress.org is temporary suspended. This does not affect our themes or plugins in any way, however, does not allow installing some plugins directly from WordPress.com repository. We have already updated our themes and included plugins in their packages. Kindly activate the theme license under Appearance ->Theme License to be able to update the Booklium theme. Once it is done, you will be able to install plugins easily. If there is still no luck, let me know so I provide you with plugins archives via email to install manually.