You may need to subscribe to a paid plan if your site is not hosted by a Moodle Partner or MoodleCloud.

If your Moodle site is hosted by a Moodle Partner (or Moodle Certified Service Provider), your site will have a Premium App plan by default. 

However, if your Moodle Partner doesn’t host your site, you may need to sign up for a plan, move to MoodleCloud or ask your Moodle Partner to host your. Please visit Do I need to upgrade to a Moodle App plan?