I think that possibly every BrE speaker has weighed in with a comment that it is abominable English to omit the "to" in "write to me". So if that is your issue, your message is received. That does not disqualify it as a correct and acceptable variation. BrE is not the gold standard for Duolingo's translations and there are just as many BrE translations which sound simply awful to American speakers. Let it be, please.