When asked to translate an English language into Spanish during a lesson, I referred to myself using a masculine adjective. Duolingo said that was a wrong answer.
Why did this happen? Duolingo never asked for my gender, so why is it telling me that I'm incorrect to refer to myself as male?
"Soy alta" is correct, so either Duo has an error that needs reporting, or there was something unique about that phrase that didn't catch your attention. For what it's worth, the Spanish for English Speakers course does have a phrase "I am tall" and the preferred answer is "Soy alto" so it's hard to say for sure what you were dealing with.
When you find a sentence that marks your correct answer as wrong, there is a button down near the bottom left of the question/answer box that says "Report Error" or "Report Problem" or something like that. You just click it and then one of the options is "My answer should be accepted". You click that, and then submit it.