"May I have an orange please? Yes."
Translation:Ga i oren plîs? Cei.
Neat, thanks! Edit: this is funny to me because "iawn" sounds more similar to "yes" and "cei" sounds more similar to "ok".
I wrote Ga i oren os gwelwch yn dda? Cei and it said there was a typo in my answer, Gaf instead of Ga, is that correct and if so why Gaf?
What you have written there is fine, and it is one of the alternative answers that should be accepted by Duo. Gaf i is just a common variation of Ga i, and the course accepts both forms.
Duo occasionally insists on correct capitalisation and punctuation. Also check that you have downloaded and installed the latest version of the app. And are you giving the answer in the correct language - is Duo asking for a translation or is it a 'write what you hear' question?
If a correct answer is still being rejected, please raise a 'Duolingo bug report'.