Read this: https://lightninglogin.live/learn

Regarding coinos: it is listed as a service that supports LNURL-auth here so I would expect it to work if you scan it via "send." Not sure why it gives an error. /cc @adam_coinos_io

I just tested our lightning login with Phoenix and it works.

edit: just tested with coinos and I also get "bad request" as an error. I don't see why it shouldn't work; the network tab also shows no errors.