As mentioned on https://backpack.openbadges.org/, Mozilla Backpack is now Badgr Backpack. Thus, we have changed the active external backpack on moodle.org to Badgr, as described in the documentation Badges settings.
If you previously connected to the Open Badges backpack, you will need to first create an account on https://badgr.io/, then go to your backpack settings page (via your preferences) and disconnect then connect to the Badgr backpack. You will receive an email from Mozilla with a zipped file of badges which you can upload to your Badgr backpack.
For further information, please see the Mozilla backpack transition to Badgr FAQs.