"Viviamo un momento di alti e bassi."
This does not make sense in English. You never say 'we are going through a moment', but would say 'we are going through a time of ups and downs' (or 'highs and lows'). Perhaps Duolingo should give the literal translation, which helps explain the grammatical construction) along with the idiomatically correct translation.
They really need to explain the fact that "alti e bassi" can mean "ups and downs".