Fedora: dnf rename repo to jami
sudo dnf update
Ring 30 - x86_64 - ring
https://dl.jami.net/nightly/fedora_31/ring-nightly.repo
must to be renamed as https://dl.jami.net/nightly/fedora_31/jami-nightly.repo
in our website download instructions then (my guess) you must to ensure the same file with both names to do not brake repos people added before.