"Sorry, I don't feel well."
Translation:Pardonon, mi ne fartas bone.
In English, we often use the verb am/is/are as part of a verb ("I am walking", "You are fighting", "He is learning"). Such a construction can occur in Esperanto, but it is used far more rarely than in English, and it is dealt with much further on in this course. Your certainly can't have two ordinary verbs together, like "estas fartas" or "havas dankas". The other thing is, it doesn't make sense to put "mal" in front of "fartas". "Fartas" means "do" in the sense of the old English word "fare", referring to the degree of success someone achieves in a particular situation or activity. "Mal" gives a word the opposite meaning, but whatever would be the opposite of "fare"?