"Have a good day!"
Translation:Ha en god dag!
Someone said on this page that "God dag" (without "Ha en") is for starting a conversation, whereas "Ha en god dag" is for the end of a conversation.. However, as we are not given a contaxt for these sentences, so we don't know whereabouts this one would come in a conversation, surely "God dag" should be accepted as correct.
Although the literal meaning is more or less identical, "God dag" is a greeting, whereas "Ha en god dag" is something you would say as you were parting ways. We tend to make exactly the same distinction in English: Expressions like this that begin with "Have a..." would never be used to open a conversation, so "God dag," which is used that way, does not work as a translation.
If you check the discussions before posting, you'll often find your question has been answered already.
Because "har" is the present form that normally translates as "is having", whereas "ha" is the infinite form and translates as "have". Moreover, as suggested previously it could be viewed as imperative here, like "Hey you, have a good day! I demand!" :D.
"Take a look at the table at https://www.duolingo.com/skill/nb/imperative" suggested by griffindd