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.