Hi Bruno I was able to login through the app using Nostr connect with both Amber and nsec.app and pasting in a raw nsec worked for me too so I haven't been able to reproduce this. Can you provide more details on where you're getting stuck exactly?
Discussion
Well in my case when I put my Coinos username and password it doesn't work, when I connect it with Nostr (nsec.app) it accepts the connection on nsec.app but I get an error message on the Coinos App. Pasting my nsec (Private Key) and submitting also returns an error.