After taking a look at coinos i'm a little intrigued it's a nostr client with their wallet attached this is more then just a wallet site since they are giving you an npub which is a nostr profile but you don't get the private key nsec to log into this npub that's sketchy. But for the purpose of using the wallet where it says enter your email for payments in nostr which is above the one that says lnurl(outdated) you would put username@coinos.io & that's it.