Translation:Waiter, the check!
I put "Waiter, check", and it said that I was missing the define article, "the". I don't think that's needed, since this isn't a complete sentence. You can say "waiter, check please" in English. I omitted the "please" in my answer only because there wasn't any Chinese please-like expression (请， 妈发你，一下) in the sentence.
At the time I wrote that, it was the answer preferred by Duolingo. It was the answer Duo would suggest if you got the question wrong, and also the answer written at the top of this forum. The preferred answer has changed back to "Waiter, the check," but "Waiter, check," is still accepted.
"Waiter, get us the check!"is rude and demeaning to the addressee. I wrote, "Waiter, check please," and got a failing grade even though I conceded to use the American "check" when I know "bill" is the correct ENGLISH word to use. Unfortunately, DL will not let me proceed or progress any further unless I slavishly comply with "Waiter, get me the check!" This is not a request but an imperious order from an officer to a recruit.
If the literal translation of the sentence is 'Waiter, check!' and DL's correct translation is 'Waiter, get us the check!', then 'Waiter, give me the check!' (and many other translations) should also be accepted, because there's no further context that would specify the number of people demanding the check (there can be a group or a person alone) or the way I/we want to have the check.
Just chiming in: "server" should be an acceptable option because: 1) earlier lessons used the term, and 2) you don't just use 服务员 in restaurants— it's more like "person in a service position," so it doesn't really translate well. Beyond that, it's polite to call out "服务员，买单," whereas the direct translation toes the line of courtesy, at least as I was taught.
I wrote "服员，买单！" instead of "服务员，买单！" as the "务" is nearly imperceptible to my western ear. It said I missed a word but didn't say which one. May the extra effort of looking here reinforce the correct phrase. On the flip side, a Chinese native speaker said "I am a service" to describe her waitress job.
Well I have seen Chinese people dont use too much good maners words as much as we use, but they use much more compliments and good luck wishes to show you appreciation. It's not the Duolingo translation that is wrong it's the cultural differences that are shown through translations :)