"He is a farmer."
Translation:He mahiʻai ʻo ia.
It's not wrong. In fact it is the answer given by the software above. If you put that an got marked wrong, there are a few possabilities.
1) You used the wrong 'okina. We are not supposed to use a regular apostrophe and the software sometimes (but inconsistantly) marks the apostrophe as wrong.
2) You made some other spelling mistake that you didn't realize.
3) A software error may have occurred.
Did you report the sentence as "My answer should have been accepted"? Do you have a screen shot of the "wrong" grading?