"Sam is new and generous."
Translation:سام جَديد وَكَريم.
This is true when the adjectives are successive (without interruption). Here we have (and) or و in between the two adjectives, so the order goes smoothly between the two languages. In fact, changing the adjectives order specially here with (and) or و does not change the meaning. However, with Duolingo, things don't go that way as probably they do a word-to-word comparison. So, the sentence might be correct, but the system in Duolingo would mark it incorrect.
This said, worth noting that successive adjectives are not always sensitive to order but it would be better to follow the reversing order rule to play it safe, specially when it comes to, for example, compound nationalities (e.g. Ahmad is a Jordanian American engineer).