fatal TLS alert on uri

a user tryn to install briar GTK reports the following issue:

I get "error: Can't load uri https://flatpak.dorfbrunnen.eu/repo/appstream/app.briar.gtk.flatpakref: Peer sent fatal TLS alert: Error in protocol version" when I try to flatpak it

original report is here: https://mastodon.social/@fav/104128177572053077