I'm on desktop now and I'm getting the same error. I tried login in using the remote signer nip05 flow on a tool I created (ngit) and I'm getting the same issue. nostr:npub1w4uswmv6lu9yel005l3qgheysmr7tk9uvwluddznju3nuxalevvs2d0jr5 is this an issue with Amber 3.1.8?
From my perspective the nip05 login not the normal remote signer login flow. Have you considered presenting a QR code, copying nostrconnect:// or nip55 nostr:npub18c556t7n8xa3df2q82rwxejfglw5przds7sqvefylzjh8tjne28qld0we7?
I suspect most Amber users don't have nip46 relays setup on the nip05. Defaulting to nsec.app relay feels centralising.