Hi Stefan,

LTI support is only included in HP5 SaaS version, h5p.com

It is a service - you'll not need to install anything to Totara, but instead of that create h5p.com account (30 free trial is available) and then plug h5p.com into Totara. 

This is quite straightforward: 

• When you get your H5P.com account, go to Manage organization and add Totara as a New Consumer in H5P.com LTI setup, then you'll get the URL, LTI Key and Shared secret needed
• Go to Totara, add H5P.com into course as external tool (activity plugin).
  You'll only need to add URL, LTI Key and Shared secret provided by H5P.com.
  

Cheers,

Jani