"Innen gibt es einen Fernseher und ein Sofa."
This might be because I'm not a native English speaker, but do you have to repeat the indefinite article (a) in English in an enumeration? I usually tend not to, but Duolingo insists it should be 'a TV and a sofa', rater than 'a TV and sofa'. Or would dropping the article in German also be acceptable, but is the answer wrong because it is explicitly included here?
There isn't a hard rule, but it's usually preferable to use the article for each item in a series to show they are separate items rather than one multi-tasking thing.
OK, "a TV and sofa" are presumably two separate things because we aren't familiar with a combination. "A camera and phone" sounds like one cell phone, however, whereas "a camera and a phone" would seem to be two separate devices.
You might say someone is "a teacher, philosopher, and member of the thought police," but say "A teacher, a philiosopher, and a member of the thought police walk into a bar . . . ."