Hi,
I just detected a totally different problem… my amazon account is registered with amazon.de, not amazon.com - I’m able to log in with the same credentials but it seems that younify can’t handle this country-based difference, since trakt scrobbler keeps showing the “sign in” button even after successfully signing in.
I assume this is because Prime Video on amazon.com seems to be different than Prime Video on amazon.de - and there’s no way to select the country before adding this.