"Her dogs are incredible."
Translation:Hundene hennes er utrolige.
I put "Hundene hennes er fantastik", and it was marked correct, with a note saying, "You had a typo in your answer" and saying I should have used "untrolig" instead. Surely that's more than a typo!
While both 'unbelievable' and 'incredible' have largely come to be completely synonymous with 'wonderful' and 'fantastic,' I think it's important to remember that etymologically, both originally meant simply 'not believable' (or 'not credible') - and that it didn't always infer a positive connotation. The original meaning of 'incredible' is less commonly used today in spoken English, except perhaps in the legal profession, or in law enforcement (e.g. "The witness is incredible,"), but it is still a good thing to it keep in mind, as you will come across it in written texts.
I'm not sure whether or not the Norwegian cognate utrolig has taken the same path of always meaning 'unbelievable in a good way'. I think this is probably also why the coursebuilders opted to keep utrolig as the primary translation - although translations containing fantastisk are also accepted.
Finally, I believe the spelling is fantastisk, not 'fantastik'. And since 'dogs' is plural, I think you'd need an -e on the end as well: fantastiske. And that's probably why you got the "spelling error" message, even if fantasiske didn't show up in the sample sentence.