Translation:I just sent you a text message.
It is more appropriate to use [have / has + V3] when talking about the events that have happened "just" or "already"
This problem is present throughout the course. Seems that the majority of the course staff is not acquainted with perfect tenses at all.
They should accept it but not insist upon it, Simple past is widely used across much of the English-speaking world in cases like this.
They should just add Chinese from dutch because after 15 years i still did not know that there was a difference between send and sent
SMS is not accepted. This is a guess-the-English-word game, not a Chinese course.
In my experience, though many second-language speakers of English say SMS, few native speakers do. Text message is much commoner, at least in Canada. Both should be accepted though.