Translation:We don't take credit cards, we only take cash.
For the English, "We don't take credit cards, only cash" is also accepted now.
But there's more going on here than just punctuation. Unlike the English, the Chinese has to have the verb repeated, though not the subject, and it can be punctuated with a comma.
For the English, if we repeat the verb we also have to repeat the subject, giving us two so-called independent clauses, as you point out. In English it's usually considered formally correct for independent clauses to be separated by either a period or a semicolon, rather than a comma as Duolingo shows it, though in casual writing it's not unusual to see a comma.* Duo's punctuation of its English example is certainly food for thought.
* Even in literary writing we sometimes see a comma where prescriptivists would put a semicolon, e.g. when the second independent clause is "finishing the thought" of the first, as is the case here. And indeed, "only cash" is really just an elliptical way to express "we only take cash" anyway.
if "We do not take credit cards, only cash" is translated to chinese it would sound more like "我们不收信用卡，现金而已" 而已 (ér yǐ) means only
the sentence given said "我们不收信用卡，只收现金" "只收" translates to "only take" so the translation is technically closer to "We do not take credit cards, we only take cash"
I agree with your technical breakdown but I'm not sure the Chinese sentence in your first paragraph would be all that likely to be used by native Chinese speakers. I'd be happy to hear from one, but I think "We do not take credit cards, only cash" would be more likely to be translated with the Chinese sentence given.
In any event, Duo does accept "We don't take credit cards, only cash", which is a fair choice.
You can use "accept" but it's weird to change from active to passive in the middle of the statement, and it's a misinterpretation of what's happening in the Chinese, which simply doesn't have to repeat the subject (whereas you've changed the subject from "we" to "cash").
I don't think that's true. I'm sure I've heard, "We don't take credit card," plenty of times. And no it doesn't really matter that "only" is in another position. The grammar is correct and the meaning is clear. You could even say, "We take cash only" and that would also mean the same thing.
It said to type what we hear. So I typed exactly "We don't take credit cards, we only take cash". The only difference between my answer and the required translation is that I put a comma where DL has put a full stop!! But DL's Chinese translation has a comma corresponding to mine!! So it must be wrong TOO!!???
I put "we don't take credit card, only we take cash" I know is not perfect English, but language is for COMUNICATION n and I understand the Chinese which is the main thing. My answer should be received, with a caveat. I know too that computer, so far, do not think. Any way in English they would rather say "Only cash" If you want to be perfect.