I adore the addition of this question. It was a big curve ball. The lesson did not cover a sentence formed like this so I repeated the audio many, many times. I could not believe it said "Hallå, ett äpple, tack!" because the lesson had not taught me that type of phrasing. I eventually just went with my gut feeling and felt very smart and pleased with myself!! Loving this course!
Swedes are less likely to use grammatical commas than Englishmen, although it's not unheard of.
As devalanteriel said it is not the place to use the word. Of course, if the person you are talking to is very close to you, friend/family member, you can say so, but here are some examples how to use snäll/snälla in different ways:
"Snälla, ett äpple" - this sound really begging
"Snälla, ge mig ett äpple" - this is better but still with a demand
"Snälla, kan du ge mig ett äpple" - much better with a question in the end
"Kan du vara så snäll och ge mig ett äpple" - this is already a question and the word snälla is turned into an adjective so this is the nicest way to use word "snälla"
It doesn't always correct, in fact it sometimes ignores typos if not important to the correct meaning. But if it complains, then sometimes for small things that make a big difference. For example if you forget to put an "s" at the end of a word to make it plural. But I also think occasionally just a hint would be enough instead of flagging an error, sometimes it would have been better to hint or flag something as an error when everything was on green.